The visual aid here is genius, and I love the piggyback note. (Once two people join in, the whole thing has a tendency to spiral out of control into a massive anonymous bitchfest.)
Spotted by Steve.
UPDATE: the sign-maker writes in to claim his handiwork! Oliver explains:
I was horrified at this state, but I also did not want to be labeled as the person that left the toilet in this state. I wanted to clean up the mess but then how would I communicate my disgust to the unknown person that actually did it? So this was my solution. Document the offense including time found and then clean up.
Like I said: genius.