It's a c. 1874-84 "pool check"— a token good for a game in a pool hall or billiard parlor. The J. M. Brunswick & Balke Co. of Chicago specialized in billiard tables and supplies, saloon furnishings, etc. Prior to 1874, J. M. Brunswick and Julius Balke were competitors. In 1884, B&B merged with the New York firm of H. W. Collender, becoming the Brunswick-Balke-Collender Co. (Source: "PBK"; a great researcher we had here on Treasurenet.com for many years.)
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