KNOX MOTOR SERVICE INC. metal advertising clip

This little springloaded metal clip advertises KNOX MOTOR SERVICE INC. on its front, with a hole on its back so it could also be hung on a hook. Nicely made of rather heavy pressed steel, it measures about 2-1/4" x 2-3/4" and is likely a product of the 1950's or so. No mfr's ID or markings.