Log 54: Impersonation - S2-E16
Visible crew/equipment: While Malloy and Reed are outside the Commander's office Malloy asks Forest about his son, and as Forest walks away we can see the actor's L-marker taped to the floor. (00:06:40)
Log 54: Impersonation - S2-E16
Visible crew/equipment: After Pete and Jim arrest the "second story men" for burglary, when Forest stops and asks, "What's the scoop?" the actor's T-mark is visible on the floor. (00:14:50)
Log 54: Impersonation - S2-E16
Visible crew/equipment: When Pete and Jim bring Freddy to the jail cell to identify the criminal, there's a T-mark taped to the floor near Jim's feet. (00:23:50)
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.