Is turning away from a sign a sign? Find out.
As discussed in Tactics for Criminal Patrol, here’s a trick that can help you spot potential drug runners in vehicles if it’s acceptable in your jurisdiction (be sure to check with your legal counsel).
Post a roadside announcing “Narcotics Enforcement Checkpoint Ahead” in an area where a U-turn is not permitted, but feasible to execute. Then position yourself such that you can spot and stop anyone who sees the sign and suddenly feels compelled to flip a U and head the other way. The illegal turn is reason to stop and their decision to change course immediately after seeing the sign is reason to have your suspicions raised.