A pothole to make it clear that a statement is honest and genuine, although it's in a context that could have it easily mistaken for an insincere comment or joke. Say someone gives a suggestion, and people respond with "I think it's a great idea!". Since that comment can be both genuine and insincere, this is a tool to help people know you are being genuine.
The reason for this can largely be seen in Poe's Law. Some people actually don't know if others are being sincere or not a lot of the time, especially where text isn't as emotive as necessary to convey the sincerity properly.
In some instances, this can even be a trope in a work, when a character is usually sarcastic or snarky, but then they get moments where they mean what they say.
In Professional Wrestling, this is often known as "shooting".
Contrast Sarcasm Mode (where you don't really mean it), Humor Mode (when you're just kidding around), and Schmuck Bait (where traps are worded as sincere warnings against falling into them). When the author is directly telling the audience that something is sincere, that's a "Not Making This Up" Disclaimer.