First off, tag the question properly. That won't help if I don't know what the book is about, but if I know that the topic of Atonement (or Twilight, or Le Morte d'Arthur or whatever) is something that will bother me, having it tagged properly will allow me to avoid it without having to seek out warning labels. Folks can add tags to their "ignore" list, check the "hide" box and avoid seeing questions related to those subjects in most places on the site without having to put in any further effort.
When (as in your example) the question itself concerns potentially-sensitive content, then do as Robert suggests and avoid gratuitously shocking language. You demonstrate this admirably in your title, which is both sufficiently detailed yet avoids any unnecessary or salacious details as to the nature of the assault.
...unfortunately, you kinda ruin the effect by including those same details as the first paragraph of your question:
This warning is problematic, since not only does it de-emphasize your actual question, it includes rather more specific detail than the question itself - and rather negates your attempt to keep it off the list of questions!
As you said originally, putting "rape" in the title should be easily avoidable - but more than that, unless your question is directly about events or terminology that might be upsetting to others, there's no real need to include it - so don't. Sometimes this will be difficult; sometimes it will be impossible... But with a bit of attention, it should be possible to treat them - and your readers - with a delicate touch and avoid undue discomfort.