In U.S. Merchant Marine officer rank insignia, the fouled anchor is the equivalent of the line officer’s star in the Navy, signifying that the wearer is a commissioned officer or in a commissioned administrative line position. As in the U.S. Navy, the officer rank is denoted by the number of stripes on the shoulder board, with a single stripe used for Ensign (O-1) and four for Captain (O-6).
When the U.S. Maritime Service was fully active (1936 to 1954), the fouled anchor was used as a branch of service mark specifically indicating Line, but it and other branch-of-service and specialty marks were enclosed in wreaths to indicate USMS provenance. Unlike the Navy, however, all officers save one wore the wreathed fouled anchor insignia (Engineering officers who reached the rank of Captain could wear the three-bladed propeller insignia). Today, private companies issue officer insignia, so on U.S. Merchant Marine vessels you may see an Officer with a Steward’s insignia (crescent moon), whereas in the Merchant Marine that mark would have been restricted to enlisted personnel and Warrant Officers (WO and CWO1).