How so? A human is more likely to use a hyphen, an AI an em dash. Same with quotes - a human is much more likely to use ", an AI “ and ”. Typography is a differentiating signal when it's used dis-proportionally more by one group than another.

Word processors (less of an issue for Internet comments, but worth keeping in mind) but more significantly iOS (at least) and I assume Android will just swap in an em dash where needed—it is automatic.

There is probably some signal, but be a good Bayesian; we have people saying “oh, this is a bot” when there’s a huge population of mobile users with smart keyboards that are the more likely cause.

Anyway, in general I find bot-hunting annoying. Comments should be handled as comments, if someone has made a bad argument, it should be taken down as a bad argument. If it was bot-generated, it is still there to mislead people. The advantage that bots have is that they have infinite patience and nothing better in their lives to do than argue, but there have always been people like that, so hopefully readers will be able to observe that persistence!=correctness.