Freeway signs warning of upcoming drug checkpoints are actually a ruse: the local sheriff sets up a checkpoint at the next offramp and searches panicky motorists who pull off to ditch their stashes. An accompanying map on the original post (click through below) gives the locations of similar checkpoints all over the USA, and warns, "if you see one of these signs, don't fucking exit."

Narcotics Interdiction Checkpoints

(via Schneier)