You are describing a "generic" poker chip. Even though some lodges and private games purchased custom "logo" chips, many simply purchased generics with a standard monogram, feeling that was protection enough from "ringing in". Some generic monograms are attributed to a particular gambling joint, but that does not mean that the chip may also have been available for retail sale as well.

These older clay monogram chips are usually worth $1 - $3 per chip when sold individually, much less when sold in sets of 100 or more. If it is a fairly uncommon monogram, like Z, X or Q, or from an unusual mold, it would be worth more, but the "J" monogram and Greek Key mold are not uncommon.