Dead dove, do not eat - this is often found in the tags or the notes of a fanfiction. It is basically a warning sign.
What the author means with this is that the reader should take a closer look at the title, the summary and the other tags, because what they can see there is exactly what's going to happen in the story. These stories mostly contain themes that are sensitive or can be disturbing for a reader.
It's an author's way of saying: "I tagged what's going to happen in the story, so don't be surprised if those things happen."