land anchor

A seatbelt that's been left outside a car when the driver closed the door. The metal end flaps and clunks against the side of the car. If enough belt is outside the door, the metal buckle drags along the road throwing up an occasional spark. More common occurrence in older land yachts with old school style seatbelts. Driver is typically clueless and doesn't hear it or doesn't figure out what that clunking noise was until he's parked and opens his door.