I've found a lot of these over the years. As several people have said, they are from a machine, typically at arcades, that you put in a coin and it drops the aluminum disk down and lets you stamp whatever you want on it. It was "invented" in Jamestown, NY (my home town) in the early 1920s (1923 is what I'm seeing online) and the earliest ones have "PAT. NO. 1455289 HARVARD AUT. MACH. Co JAMESTOWN N.Y." in the center on one side. I've found them with "Good Luck" and a horseshoe, flags, "1939 Worlds Fair NY", and other devices in the center. Apparently some of these machines are still around, although I haven't seen one since the late 1970's.
Scott