I haven't seen your specific chip, David, but here are pics of four different types of concentric circle chip molds. See if your chip matches one of these types. The first three chips have the circles only on the center section. On the last chip, the Mapes, they cover the center section and the outer section beyond the SmallKey design.

If others have different variations on the theme, I'd be interested in seeing scans of them.

DonL