It's a standard punctuation mark available on Android/iOS/macOS keyboards, and automatically inserted into text by widely used software such as Microsoft Word. You guys are acting like it's an obscure Unicode character that GPT just spontaneously started using out of the blue, and ignoring the obvious answer that it's common in LLM output because it's common in training data. The burden of proof is on anyone claiming that it isn't common.

I was referring to social media spam. It would be a simple way to defuse people citing the use of dashes as "proof" that your spam was spam and having the hivemind bury it. You can't ensnare gullible readers if they never see your comment to begin with — not that following an absurd blanket rule of categorizing em dash usage as AI output has anything to do with whether or not the reader is gullible.