We get banned if we don't mark our fics appropriately.
Read Terms of Use to know more about this

I think that pretty much anything that you wouldn't want a young person to read- things like extensive detail about violent fighting/abuse scenes, ual scenes, and intense horror and potentially mind-scarring and psychologically disturbing for someone younger than 18.

If you just imply ual scenes in the way that someone young can still read it with an innocent mind (like, idk, bananas and cream and stuff like that lol), then it should still be ok. As well as a couple swear words, but i guess it would be wise to put a disclaimer before the start of the story.

If you are describing violance, too intense kissing scene, etc. But usually aff marks it by itself. :)

Usually things like , extreme violence, and vulgar language would be a red flag for putting the rating to m. However, if it's a simple fight scene or if you use one or two swear words, it doesn't need to be put as rated. But as soon as / is written, put it on M. Alluding to , you can probably get away with not rating it as M, but it's more of a judgement call on your part. If it's like a sentence talking about it, then you're probably fine, but if you're mentioning stuff like that throughout the chapter, then rate the chapter as M.

It also may depend on the subject matter as well, especially if you're writing something psychological or are alluding to things like abuse and whatnot.

Depending on the fic, if only a chapter or two are going to be rated, just rate the chapters with the M label. But if the whole story is rated, or if you feel the subject matter to be more than what a PG-13 label would have, then rate the whole story as M.