Just as a joke one time.....
I got ahold of a label maker where I use to work, and on the inside of the stall in the men's bathroom I wrote:
"Please don't lick here" and put it in various places in the bathroom....the toilet seat, ceiling, actually onto the toilet paper, the towel dispenser, the door knob.
And of course the implied meaning was that this had happened consistently before, and had to stop!