ensign (n.)
late 14c., via Scottish, from Old French enseigne (12c.) "mark, symbol, signal; flag, standard, pennant," from Latin insignia (plural); see insignia. Sense of "banner, flag" is c.1400; that of soldier who carries one is first recorded 1510s. U.S. Navy sense of "commissioned officer of the lowest rank" is from 1862. French navy had rank of enseigne de vaisseau since at least early 18c.