Van Nuys Division: Pete's Mustache - S6-E7
Continuity mistake: The officers are leaving the station on patrol. There's a police car parked in the outer lane of the exit. Next shot, they're driving out of the same lane, and the car is gone.
Factual error: 19 1/2 minutes in. They pull over a car and run the plate. Malloy tells the driver the car is registered to a Volkswagen. He should have said the plate is registered.
Answer: You probably need to be more specific about which car or episode you're talking about, but if I had to guess, it sounds like you're talking about "curb feelers." Most people have to park on the right side of the road (passenger side), so the wires or springs would make a noise when they hit the curb, letting the driver know they're close enough to the curb without hitting the tire against the curb.
Bishop73
S5 Ep5 "Training Wheels": Adam 12 stops a VW van. Their Matador car has a curb feeler on the left front of the car.
Correction: That's the right-hand side of the car.
Probably for one way streets. When they were popular, I saw them on front and rear. They were the mustaches and eyebrows of the day.