Reason has a brief clip (at the end of this post) on a town's police cracking down on an individual who carried a sign warning drivers of speed traps.
What this man did, however, is a public service. Indeed, provided he might have had other things to do with his time, it's downright heroic and should be emulated.
Because he's alerting speeding or careless drivers that it's in their best interest to drive carefully within the speed limit. This serves the public, and the drivers themselves, by creating safer traffic.
Police should be grateful. Indeed, they should deploy plainclothes officers to do this kind of thing, randomly, throughout parts of town. They could even announce the program to the public that they'll be doing it, and even announce that the signs will be lying 50% of the time.
Wouldn't that encourage drivers to obey the traffic laws and avoid getting pulled over?
If safety, not ticket revenue, really was the end-game of traffic laws and police patrols, this should be a no-brainer.