Might have more luck if you switched to the lazy em dash that is just two normal dashes.
I think that the people trying to call out slop are doing more to hurt those competing with AI than AI itself.
Like someone using AI to produce stuff might get annoyed at being called out but then will probably just think "ok, gotta prompt it to avoid these signs" or waits for a newer model or just dgaf that people notice it's AI.
But people producing their own things and being accused of it being AI must feel pretty fucking discouraged that not only do they need to compete with something that can output things in a fraction of the time, but even when they do, some people accuse them of being what they hate.
For text content, IMO it should be taken based on what is said rather than who (or what) said it. If it's useless slop, there will be things to push back on other than the formatting. Plus, it wouldn't surprise me if you could just add "format it like a low effort forum post" to the prompt to get it to avoid some of the more obvious formatting tells.
Also, if people religiously call out AI slop when they see it, that could be used to automate training similar to what I'm sure happened to drastically improve programming capabilities, which will accelerate the speed at which they can become indistinguishable from things produced by real people.