distinguishing flag

1 :  any of certain flags flown to indicate the presence of an officer of high rank or of the holder of a high governmental office —used in the British navy and the U.S. Army — compare personal flag

2 :  a flag flown to identify the headquarters of a major unit of the U.S. Army that does not have an organizational color or standard

3 :  a flag indicative of the ownership of a vessel (as the house flag of a commercial ship or the private signal of a yacht)