They are generic monogram clay poker chips made by the US Playing Card Co. in the first half of the twentieth cenury.

More specifically, they are referred to as reverse die-cut inlays (so named by the grandfather of die-cuts, Steve Passalacqua).

These chips should be found for about a dollar each. When racks of 100-300 are up for sale, $0.40 to $0.75 each is about right.