There was an example on here recently where an AI PR to an open source literally had someone else's name in the comments in the code, and included their license.

That's the level of tell-tale that's its just stealing code and modifying a couple of variable names.

For me personally, the code I've seen might be written in a slightly weird style, or have strange, not applicable to the question, additions.

They're so obviously not "clean room" code or incredibly generic, they're the opposite, they're incredibly specific.