Exciting graffito

While taking a break to use the bathroom in the library, I discovered written upon the stall door the exact text needed to pull my thesis together.  But, how do I cite it?  I looked through the MLA, APA and Chicago guides, but there is no listing for bathroom graffiti.  How should I cite this?

Well aren’t you a clever person?!  And thanks for informing us about this vandalism; I’ll relay the information to Housekeeping so they can remove it.  By the way, this is exactly the sort of question our reference librarians answer at Ask Us Now!

I’m a bit embarrassed to admit that I’ve been straining with this one, because of my strong urge to express myself with an answer worthy of your question, an answer of sufficient girth and gravity to allow you to easily plop the citation into your paper.

You’re correct that APA and MLA don’t offer guidance on citing graffiti specifically. I recommend checking The Chicago Manual of Style on Informally Published Material.