A common sign that means, contrary to popular belief, that it is illegal to drop off trash in the specified location. This trash may or may not include human fecal matter. This sign will never cease to amuse high school kids.
Joey: "Hey, guess what guys? Check it out! I just put up a "No Dumping" sign above the shitter in the boys' room!"
Marty: "HAHAHA!!! All right! Awesome joke! You da man!"
Kenny: "Yeah dude, that's totally rad!"
"this is not a drill message" -- implying the following messages are not simulation or exercise related message but of vital and usually life/death importance
"Charlie one five, Zulu four zero, no duff message, Zimmerman is down, Zimmerman is down"
"Zulu four zero, charlie one five, medic on the way"