Shit. I flagged an academic paper a while back on my old computer and now, of course, I can't find it, but it linked current notions of ratings and warnings to historical accounts of authors and literature and the need for secrecy in writing because, way back when, one couldn't be or write about the gay experience because everyone would be clutching their pearls and, y'know, sending them to jail for writing such "explicit" material.

Basically it discussed how, through time, all those "secret handshakes" in literature that certain people knew how to read but that were layered in such a way that "commoners" couldn't tell what was really going on, how those evolved into warnings and ratings, if that makes sense.

It focused more on old school literature and the history of film censorship and I don't remember there being a lot, if any, focus on internet literature and fandom, but the general idea might be interesting in this context?