The Steward’s Department aboard a Merchant Marine vessel handles the tasks associated with three now-discontinued U.S. Navy ratings: Stewards, messman, commissaryman. Among these are the preparation and serving of meals, including requisitioning and storage of foodstuffs and related items; cleaning and maintenance of Officers’ living quarters and the Steward’s Department’s areas; and oversight of storage areas for security and cleanliness.
A crescent moon seems to be an odd choice of an emblem to represent these tasks, but the selection has more to do with tradition than anything else. Today’s handful of Merchant Marine branch-of-service insignias—the equivalent of a Corps device in the U.S. Navy—are the same as those worn by Officers in the United States Maritime Service, which was instructed to use the ranks and ratings of the Coast Guard when it was authorized by the Merchant Marine Act of 1936.
The Coast Guard had used a letter “C” that strongly resembled a crescent moon for its Stewards and Mess attendants—but you could tell it was a letter, not a shadowy mon. The Merchant Marine’s Steward insignia, however, more closely resembles the insignia the Navy used for its Ship’s Cook rating, which was merged with Chief Commissary Steward, Ship’s Cook (Butchers), and Baker to create a Commissaryman rating in 1948.
But why did the Navy use a crescent moon for this rating? The use of this shape to represent food and other essential supplies is said to date as far back to Babylon and Rome, but it was during the Civil War that the U.S. Army adopted it and, by World War I, it had become an internationally recognized symbol for food and rations.