Not many and not obviously. A dropped apostrophe, a sentence that doesn't quite land, an em dash swapped out for a bracket. Wired covered it last month as an anti-AI literary counterculture, and the logic is what you'd expect. Clean prose reads as machine prose now. So people are roughing theirs up to prove somebody was there.
And I've got form here. I banned em dashes from my own writing over a year ago, well before it meant anything, purely because I thought I was leaning on them. So that now reads as a credibility strategy. I'll be taking the credit.
But it won't work
And it won't work for the dullest possible reason. Give it six months and the models will be writing in fragments with the odd missing apostrophe, because that's what the training data is about to look like, and then we'll all need a new tell. Somewhere out there is a person whose entire brand becomes the semicolon.
Which is irritating, because it's the one part you can't fake with punctuation.