from a quick search, it is unknown exactly when these were counter stamped, with dates ranging from the late 50's (1958) to the early 60's. they might have been part of a promotion, but the Ford Company did not do these. Most likely it was a very bored worker, or a dealer promotion. The dealer promotion might have been, find a coin and win a car, but there have been quite a few found so I do not know if that would be fiscally feasible. Either way it is a cool find.