Revealing mistake: Halfway through the show, the officers get a flat. As Malloy is getting ready to jack up the car, Reed starts using the lug nut wrench to loosen up the nuts. He repeatedly turns the wrench clockwise, which would tighten the nuts.
Log 51: A Jumper, Code 2 - S1-E19
Other mistake: Halfway through the show, the officers walk across the street to talk to some young toughs. The school sign painted on the street is spelled "Schol".
Visible crew/equipment: When Reed asks Walters how many kids he has, the moving boom mic casts a shadow on the lockers at the top, left side of the screen. It appears again a few shots later. (00:00:50)
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)
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.
Other mistake: Malloy is the training officer and Reed is the trainee for what appears to be years. A major part of training as a cop is to get hands-on training to drive in emergency situations, but Malloy always does, except when he has an invalid license or needs to move the car.
Continuity mistake: In the opening scene, an officer is yelling at Reid for trying to give him a dog. There's a gun belt hanging on the locker next to Reid, Malloy comes in and it's still there. Next angle, it's gone.
Continuity mistake: About 3 minutes in, Malloy is practicing driving on a course with an instructor. Most of the outside shots show only a driver in the car.
Log 54: Impersonation - S2-E16
Continuity mistake: When Reed and Malloy go to the boxing gym's office the first time, the name on the door's glass window is spelled as "Fredie" and he's the owner and manager, but in the end credits James McEachin's first name is listed as "Freddy." (00:03:15 - 00:24:15)
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)
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
Other mistake: They deal with the owner of a gym and his jersey says "Rivers" but the building says "River's". Is his name Rivers or River?
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.