As for most electrical contacts, the finish is gold zinc. The items itself is called a "Strap, Radio Receiver Hood Bonding". There may have been static in the radio from movement in the hood by metal to metal contact. (Other reasons - It prevents the car from being tracked by radar. No? OK, it keeps the hood from turning into a transmitter. No? OK, it's a device used in area 51 or Roswell, NM cars only.)
Jim