Frequently how it shows up on "No Stupid Questions" is that they're pushing a bigoted agenda under the guise of "I'm just asking a question and everyone's attacking me for it." Like if someone came to No Stupid Questions and asked (and this is just an example, not my position at all) "why is there so much trans propaganda on Lemmy?" or whatever. (And in the thread when people are like "you're a bigot" they respond with "I didn't say anything bigoted. I just asked a question.")

But yeah. Like what Xtallll said, it's more generally using language/symbols that for the in group is a reference they'll all get but for everyone else at least retains an air of plausible deniability. Often it's done by politicians (particularly right-wing politicians) to try to straddle the fence between the extremits and more moderates in their party. If a politician speaks in support of "states' rights," they'll get the vote of the extremists who know that "states' rights" actually means racist policies and also the moderates who still think or perhaps are still deluding themselves that it means somthing vague but more benign.

urban dictionary Dog whistle is a type of strategy of communication that sends a message that the general population will take a certain meaning from, but a certain group that is "in the know" will take away the secret, intended message. Often involves code words.

Republicans say they want to make civil rights for gays a state issue, which is really just a dog whistle strategy for saying that they will refuse to grant equal rights on a federal level.

An actual dog whistle sounds at a frequency (?) inaudible to humans but is heard by dogs. The “secret phrase” can be said out loud, but like the whistle, only the big dogs hear it - the rest of the humans don’t. Does that make sense? It’s used as an analogy.

It's a shibboleth, a way of asking a question that people who share your ideology will recognize as pushing it, while those who do not will not. This is like a dog whistle that can be heard by dogs but not by humans.

In question form it's also often subtle propaganda, asking a question that presupposes something controversial, like "Why are trans players allowed to win so much on sports?" where the simple shibboleth might be "Should trans players be allowed in sports?" Both are confronting the same point, but the former assumes a trend that has not been demonstrated, while the latter simply assumes some reason without making it clear what the reason is.