Visible crew/equipment: In the scene showing Officer Malloy shortly after he enters the inside of the supermarket, a crew member is visible in a back room/hallway of the supermarket.
Credit Risk - S7-E10
Other mistake: Reed is running license plate numbers over the police scanner, looking for a hit-and-run culprit. The plate number he is looking for comes back on the radio as owned by a woman and is on a tan 1974 Ford sedan, but when the officers go to the woman's house and see the damaged car with that license plate, it's not a tan Ford, but a tan 1974 Chevrolet Caprice.
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.