Oh, that's what caught you imagination!
ROTFL!!!
Now that you mention it....There were a few of public restrooms that were I saw some strange signed posted.
"No open Flames"
"Strike no Matches"
"Warning room not vented"
"NO DUMPING"
"Bad aim? Take it outside."
I wondered of the first two were posted for fire safety or to avoid methane explosions.
The next to the last one wsa a standard sign that can be purchased in a hardware store to tell people not to discard any trash in the posted area. I think that in the case of a public restroom that management were posting the message to mean don't leave you trash in the restroom, but based on another semi-vulgar slang, it take on a whole different meaning in that location.
The last one was posted in an establishment where the management did not speak english very well. I think they meant to say, "If you are going to make a mess, get out and go someplace else". But that is not how that sign said, and I don't think they would have liked it if the gents did follow that instruction to the letter.
Pangor