Why do bank employees put magnetic signs on their cars (prominently parking in the lot) implying they are "Security?"?

I have driven past the bank in the morning when one of the selected employee is placing the magnets on the front doors of her car. On various days, the magnets are on different cars.

I am hard-pressed to believe that this is a deterrent to crime and just seems kind of silly to me. Do any Flutherites work at a bank that does this? Why is this practice in place?