If they wanted to watermark (I always felt it is irresponsible not to, if someone wants to circumvent it that's on them) - they could use strategically placed whitespace characters like zero-width spaces, maybe spelling something out in Morse code the way genius.com did to catch google crawling lyric (I believe in that case it was left and right handed aposterofes)
Which could be removed with a simple filter. em dashes require at least a little bit of code to replace with their correct grammar equivalents.
Just replace them with a single "-" or a double "--". That's what many people do in casual writing, even if there are prescriptive theories of grammar that call this incorrect.
> em dashes require at least a little bit of code to replace with their correct grammar equivalents
Or an LLM that could run on Windows 98. The em dashes--like AI's other annoyingly-repetitive turns of phrase--are more likely an artefact.
The replacement doesn't have to be "correct" -- does it?