Comic book lettering has some grammatical and aesthetic traditions that are unique. What follows is a list that every letterer eventually commits to his/her own mental reference file. The majority of these points are established tradition, sprinkled with modern trends and a bit of my own opinion having lettered professionally for a few years now. The majority of these ideas have been established by Marvel and DC, but opinions vary from editor to editor, even within the same company. I'm often asked to bend or break these rules based on what "feels" best, or more likely, the space constraints within a panel.
As a letterer you're eventually going to see scripts from writers who don't know these standards or aren't interested in them. (Although I find the best writers are well versed in these points.) It'll be up to you to spot and fix these in the event that the editor misses them.
Note: Underlined terms reference another entry in the article.
An asterisk appearing in dialogue references an editor's note; a caption somewhere else in the panel or on the page. These generally inform the reader that more information can be found in a separate issue or comic book, or explain an acronym.
If at all possible, a balloon tail should point to a character's mouth as if an invisible line continued on past the end of the tail to their face. Pointing it in the general area of the character, (their hand, leg, etc.,) should be avoided if possible. A tail should terminate at roughly 50-60% of the distance between the balloon and the character's head.
There's almost no plain bold in comics dialogue. Typically, bolditalic is used when emphasis is placed on a word. Occasionally you may use a non-traditional dialogue font that will actually work better with plain bold. I've found this most often comes up with indie/underground books with their own very specific look and feel.
Similar to butting balloons, this stylistic choice consists of the white interior of a balloon breaking into the white of the panel gutters. This is determined completely by preference but seems to be more prevalent in hand lettering. I suspect this is because doing it digitally generally adds an extra few steps that can take time to do properly and cleanly. But remember: If the gutters in a book aren't white, you may run into the problem of not being consistent throughout.
Breath Marks (AKA, Whiskers, Fireflies, Crow's Feet)
Breath marks are usually three little dashes stacked vertically that come before and after some sort of cough or sputter. The word with the breath marks around it may be italicized, lowercase or bold. There seems to be no hard and fast rule for these. I generally italicize and if the coughing gets really bad, I use bold. If you use an opening and closing set with no word in between, you get a symbol that looks like a tiny bursting bubble that indicates death or unconsciousness of a character. This is often used to end the text in a wavy balloon.
Burst Balloons (AKA, Shout Balloons)
Burst Balloons are used when someone is screaming their dialogue. They tend to be more irregular and chaotic than the radio balloon, perhaps with a heavier stroke. Burst balloon dialogue is often bold with certain words enlarged or underlined for even more emphasis. A less punchy variation on the burst balloon is a regular balloon with a small burst where the tail meets the balloon.
Butting Balloons (AKA, Anchoring, Top-lining, Side-lining)
This is the best weapon in your arsenal to combat space restraints. Essentially, some part of a balloon is cropped flat and placed against the border. Useful when a writer has given you the Gettysburg Address and the artist has given you a thimble to fit it in. Left aligning, centering or right aligning the text against a border is a great visual change of pace in any book.
There are four types of captions in comics: Location & Time, Internal Monologue, Spoken, and Editorial. Location & Time captions can be in the same font as your dialogue only inside a caption box and italicized. Alternately they can be blocky, sans-serif fonts to indicate locations and time stamps. In many cases these are italicized and can be lowercase as well as having drop caps or outlines. Internal Monologue captions, largely replacing thought balloons, are the inner voice of a character. These are typically italicized. Spoken Captions are the vocalized speech of a character that is off camera. These are not italicized but make special use of quotation marks. Finally, Editorial captions feature the voice of the writer or editor and are also italicized.
This is probably the biggest mistake seen among amateur letterers. An "I" with the crossbars on top and bottom is virtually only used for the personal pronoun, "I." The only other allowable use of the "crossbar I" is in acronyms (like, F.B.I). Any other instance of the letter should just be the vertical stroke version. Although I would debate it, you occasionally see the "crossbar I" used as the first letter of someone's name.
There is no Em or En dash in American comics. It's a double dash and it's only used when a character's speech is interrupted, or in place of a semi-colon; which is not used in comics. (Em or En dashes are occaisionally seen in UK comics lettering.) The double dash and the ellipsis are not interchangeable, even though many writers use them interchangeably. For the record, there are only TWO dashes in a double dash. It sounds like common sense, but you'd be surprised.
Double Outline Balloons
Double outline balloons serve the same purpose as a burst balloon; to add emphasis to dialogue. The tail of a double outline balloon can connect to either the inner or outer balloon and the background balloon usually sports a color fill or a heavier stroke. Variations are numerous and up to the letterer.
Drop Caps / Decorative Caps
Drop caps or decorative caps, are an enlarged or embelished first letter in a caption. They come in a wide variety of styles and sizes, and are most often a stylistic choice by the letterer. Sometimes they begin every inner monologue caption, or just the location/time captions.
The ellipsis is used when a character's speech trails off. If a character is speaking, trails off, and then resumes in another balloon, you should always end the first dialogue with an ellipsis and then begin the second dialogue with an ellipsis. Another allowable use is when a character's speech trails in and out, or they pause due to physical distress. Injured characters or those soon-to-be unconscious often make good use of this in wavy balloons. There are only THREE periods in an ellipsis. Again, you'd be surprised how often you see four or more.
When a character speaks in a foreign language, each block of dialogue is begun with a "less than" symbol and ended with a "greater than" symbol. Often, the first appearance of the language will also end with an asterisk to denote an Editorial Caption that explains the language from which it is being translated.
Hollow Sound Effects
A relatively recent trend in sound effects; hollow sound effects have an outline, but the center is see-through, so that focal art can still be viewed. This is most often reserved for instances when space constraints, or need for impact demand it. I've never been a fan, and almost always try to find an alternative solution.
There's no set rule on hyphenating a long word to make it fit a balloon, but it's generally accepted that you should avoid it if at all possible, and even then, only if it's a compound word that breaks well.
The use of italics is quite varied: Italic dialogue is used for internal monologues, traditional-style locator & time captions, editorial captions, in thought balloons, for words that are in a language other than English, or for any instance where a voice is being transmitted through a TV, radio, communicator, as in a radio balloon. Occasionally, you'll see italics used for non-verbal words like "Uh," or "Huh", or in conjunction with someone who is whispering. Italics are also used for non-English words and the titles of movies, books, etc.
Balloons directly joined together are generally of the same thought process. Two or more expressions that are of the same topic should be executed this way. This rule is most often broken when space constraints don't permit it and you have to use a connector.
Joining Balloons with Connectors
There are two instances where this is used. The first is when a character says two separate ideas expressed one after the other. The second instance is when two characters are speaking in a panel and the conversation goes back and forth between them. Their balloons will be staggered and joined with connectors. This rule is most often broken when space constraints don't permit it and you have to join the balloons directly.
Music / Singing
A lone music note generally denotes whistling. You often see one or two music notes in a dialogue balloon, which indicates singing. Sung dialogue is often italic and follows a wavy baseline.
Numbers in dialogue should be spelled out unless they're a date, designation, part of a name or a large number. A good rule of thumb is that any number over twenty can be numeric.
When a character speaks from "off-camera", the tail of the balloon generally butts against the panel border. Some editors prefer to simply have a tailless balloon. These balloon tails can be a plain arc shape, or an S-shape.
Overlapping Panel Borders
Overlapping a balloon over a border tends to look a little amateurish, but can be necessary due to space constraints. If at all possible, you're better off butting balloons to a border. If you really have to overlap a border, continue to do it throughout the book as a stylistic choice or it'll really stand out.
Question Mark / Exclamation Point
This should only be used for a shouted question. It's a loose rule that the question mark should come first. Marvel insists on it, and I agree, since the text is probably already bold or enlarged (indicating shouting) so the only visual clue a reader has that it's also a question, is the question mark, giving it priority.
Quotation marks are used for spoken captions when a character is speaking off-camera. In the event that there is more than one caption in the series, you should begin each caption with an open quote, but ONLY use the end quote on the final caption in the series. If two or more characters have spoken captions, end quotes should appear as each speaker finishes/before the next one begins. Punctuation on the last line of a quote should always appear before the closing quotation mark. Some editors ask that an end quote be used at the end of a page even if the captions resume on the following page.
Radio Balloons (AKA, Electric Balloons, Broadcast Balloons)
These are also called, "electric balloons". Whenever speech is transmitted through a radio, TV, telephone, or any type of speaker, it is italicized and in a radio balloon. The most common version is a uniformly spiky balloon with a lightning bolt tail to the source. Over the decades, letterers have introduced other types of balloons have started to become commonplace (see examples) - probably to differentiate between a radio balloon and a burst balloon.
Used for title copy and sound effects, "roach chew" are those little lines within letters that lend a grimy, aged feeling.
Most often used for the dialogue of monsters, and in conjunction with monsterous fonts for a creepy or distorted voice.
Small Dialogue / Big Balloon
A reduced font size is used when a character mutters something, says something to him/herself, or speaks sheepishly. Often you'll see a lot of space left in the balloon. This is sometimes used for whispering.
Sound Effects (and Sound Effects Punctuation)
Noises that aren't speech, are displayed in type styles that should help convey the intensity and properties of the noise. Letterers are split over whether sound effects should be punctuated with exclamation points. With very few exceptions, I tend to think adding punctuation to effects makes them look childish and cartoony; I almost never punctuate them unless that's the goal.
When a character is speaking off-camera, from behind a door or from inside a building, for instance, the tail of their balloon terminates at the point of origin and has a small, multi-pointed burst at the end of it, called a squink. Letterers often take creative license with the burst, sometimes giving it curves, making an irregular star shape, or even using something that resembles a pair of breath marks.
When a balloon or sound effect brushes against (but doesn't overlap) another lettering element or a line in the inks, this is called a tangent, and should be avoided at all costs. They cause visual dissonance and are an often bemoaned nuisance for letterers.
When a character is speaking telepathically the dialogue may be italicized. Old-school telepathy balloons look like a thought balloon except they have breath marks on opposing corners. These days, many letterers opt to abandon the traditional style and get creative with these.
Thought balloons have fallen out of fashion in recent years in preference for internal monologue captions. Text in a thought balloon can be italicized. The tail on a thought balloon is made up of smaller bubbles and should point towards a character's head (not mouth, as in standard balloon tails). Generally you should have at least three little bubbles of decreasing size that reach toward the character.
Generaly used when a character is in physical distress. Dialogue is usually stilted and broken by ellipses and the balloon and tail are shaky. As a character descends into death or unconsciousness, their dialogue may get smaller and smaller and end with a double set of breath marks.
Traditionally, whispered dialogue is indicated by a balloon with a dashed stroke. More recently accepted options are, a balloon and dialogue in a muted tone (grayed-out), lowercase text, or as small dialogue/big balloon. Italics are a possibility as well.
Special thanks to Todd Klein, Clem Robins, Scott Allie, and Jason Arthur for their time and contributions.