We have an NSFW category for stories that contain more-than-direct references to sexual topics or descriptions. Some users also use it for stories that go above and beyond the usual gore descriptions. We will probably be reviewing and editing that policy to be a bit more clear cut soon.
However, this topic has less to do with our direct policies and perhaps more of a generally positive/healthy warning to put at the start (and perhaps might be relevant to how FANDOM scrutinizes this platform). I think you should still place a trigger warning at the start since plenty of authors here already do this, and you have very little to lose by doing so. You can do this using the author's note template while editing in Source - just type {{AN|Description of possible triggers}}.
