Common slang umong military enlisted to salute an approaching person in uniform when uncertain of their rank. Better to be safe than sorry. More common with the NAVY as Chief Petty Officers have gold anchors on their collars and are often mistaken for gold oak leafs (signifying a Lieutenant Commander or Major).
Bill- "Don't look now, but here comes an officer"
Larry-"No, it looks like a Chief Petty Officer
Bill-"When in doubt, whip it out. Better to be on the safe side then to ignore him if he was an officer".
*Both saluting-"Good morning sir".