Chop Mark. A custom in the orient of stamping a coin, usually a large silver foreign coin, with a punch indicating its acceptability of fineness and weight. The chop mark was

a counterstamp applied with a punch by a banking firm. A different punch was used by each banking house, and since this was done at each bank transaction the coins soon became cluttered with many "chops" as they circulated. The practice, called shroffing, continued for 150 years, beginning about 1770, brought about with increased Far Eastern trade. Payments were made with silver coins (as Mexican pesos) but the Orientals treated them as bullion rather than money. The practice ended in the 20th century when Western style coins and coining were introduced into the orient. Countries there began striking coins with Western technology and equipment, at which time the Orientals began accepting coins by denomination rather than as bullion.

Silver trade coins, as U.S. trade dollars, were widely accepted and chop marked. The punches were usually Chinese characters, but symbols (as a rosette) were also used. In cataloging, the chop marked item is noted collectively without identifying the individual marks. The term is also called shroff mark (see shroff). Trade coins without chop marks, are said by numismatists to have a clean field.

Reference:

NE42 {1982} Doty, p 51-52.