Posted 29 September 2010 - 07:44 AM
In John Stacey's book U.S. Navy Marks on Marine Uniforms, published by the author, he shows this mark in Plate IV along with other marks that he calls "marks with no clearly attributable use" on USMC uniforms.
John has found regulations, directives and photos of many USN design "marks" used on USMC uniforms and lists those in his book.
As Steve states above, and as was common practice by USN/USCG uniform insignia producers, they often produced insignia on rumors and hunches that insignia were going to be authorized and needed.
John's books are published by the author, John A. Stacey, 2880 Smith Point Rd., Nanjemoy, MD 20662. His prices change for ASMIC members, show specials, mailing costs, etc., so I won't attempt to quote any prices for him. He's a great guy, contact him.