A policeman had a perfect hiding place to screen speeding drivers. But one day, everyone was under the speed limit, the officer investigated : a 9 year old boy was standing on the side of the road with a huge hand-painted sign which said "SPEED CAMERA AHEAD."
A little more investigative work led the officer to the boy's partner in crime, another boy about 200 meters beyond the speed camera with a sign reading "TIPS" & a bucket at his feet full of coins.