Thought Caption

Captions have been used in the comics medium to convey narration, description, and setting. It has become a recent trend in Western comics, starting from approximately the Dark Age, to represent characters' thoughts with captions as opposed to thought bubbles, a comic-book equivalent of the cinematic technique of first-person narrative voice-over.

Scott McCloud said it best in Making Comics:

"[Thought] captions seem to acknowledge the audience in a way that [thought] balloons don't, as if the character was sending their thoughts directly to the reader, and they can give the text an extra level of intimacy. They also don't require the thinker to be in panel to show where the thought originates from, so they can appear an panels that are framed from the thinker's point of view. Such 'thought captions' are usually in present tense ... and first person ... but past tense narration ... can cover a lot of the same ground." (155).

Note that in manga, this is essentially the norm, as characters' thoughts are generally not shown in thought bubbles though they are not necessarily in captions and can be simply written on the page detached from the characters.

When captions are used to represent the thoughts of different characters, it becomes an issue to indicate to which character the thoughts belong. Measures often taken to do so usually involve using different fonts for different characters, different caption colors for different characters, or different font colors for different characters.

Not to be confused with when a character's writing (e.g., Rorschach's journal) is represented in a caption or captions that don't represent thoughts.

Examples of Thought Caption include:

Dark Horse Comics

Hellboy initially employed this trope but eventually dropped the first-person narration.
- The Doom Comic employs this both as a narration device and to represent the protagonist's thoughts.

DC Comics

V for Vendetta, from the second part onward.
Batman: Year One subsequent stories within the Year One framework, distinguishing between different narrators with different fonts.
Mostly averted in Watchmen, which does not have any narrative devices to show characters' thoughts, let alone captions, except in Chapter IV, which reveals Dr. Manhattan's back story. However, this trope is played straight in the comic-within-a-comic Tales of the Black Freighter.
A rare lampshading occurs in Ambush Bug: Year None where Ambush Bug mourns the loss of thought bubbles as opposed to thought captions. In one scene he wakes up to discover his thoughts are in balloons again and there is third-person omniscient narration in the captions and suspects he's in the past.
Superman/Batman used this trope to illustrate the differences in the two title heroes. For instance, Superman's caption while fighting the Parasite might read "It's a shame that someone with that much power went down the wrong path in life. Maybe this time he'll get back on the right track." While Batman's will read "Parasite, another example of a career criminal with no chance of reform."
In Booster Gold it goes a little further than just different color and font, showing a little symbol in the caption to let you know who it is. Rip Hunter's thought captions are red with a green infinity symbol while Booster Gold is yellow with a blue star.
- This actually seems to be a line-wide stylistic choice in DC comics, as it's been seen in Superman, Batman, Wonder Woman, Green Lantern, Flash, etc.
The third Flash is notable in that his Catch Phrase/Badass Creed usually only appeared in the Thought Captions. "I'm Wally West. They call me The Flash. And I'm the fastest man alive. "

Eclipse Comics

Scott McCloud's Zot uses this sparingly, namely in the early part of the series (viz., the opening monologue) and the later part (the characters' escapist monologues).
- In Making Comics, McCloud points out this trope and discusses Thought Captions versus thought bubbles at length (see the quote above).

Marvel

Deadpool. In fact, he currently has two: one "normal" (yellow, with handwritten text, like his speech bubbles) and one more rational (white, with typewriter-like text), which dialogue between themselves as much (or even more, Depending on the Writer) as they do with 'Pool. It is hinted that each of them represents one of his brain's hemispheres, as seen in a Dark Reign story involving him fighting Bullseye-as-Hawkeye: he has an arrow stuck in his head that does not let him think straight. When he removes it, his yellow boxes come back normally, but his white box blabs incoherently for a while.

White thought box: Be the meat
Deadpool: Say what?
Yellow thought box: It was the other half. Ignore it.

- ...and Agent X.
Madrox in X Factor, who currently sees himself as a Noir detective rather than a superhero, and therefore has a Private Eye Monologue.
The Matt Fraction Defenders series has an unnamed narrator who speaks directly to the audience in these. They employ a very familiar tone, as if someone were letting us read his/her thoughts.

Slave Labor Graphics

Johnny the Homicidal Maniac employs this in a few instances with an internal monologue from Johnny and Johnny's ~~final~~ soliloquy (before he says it aloud).

Top Shelf Productions

Used throughout Craig Thompson's Blankets to draw biblical parallels from events in his life.