For Service coats the collar insignia consist of bronze metal disks with a raised rim, worn on each side one inch from the neck opening. The disk on the right side bears the letters “U. S.” with the number of the regiment or, where there is no regimental organization, the number of the unit if there is one. To designate men of the Volunteers, Reserves, National Guard and National Army the letters “U. S.” have superimposed upon them the letters “V,” “R,” “N. G.” or “N. A.” respectively. The disk on the left side bears the special device of the corps, department or arm of the service with the letter of the company, battery or troop below it, except for the Engineers where the letter is above the device. The special devices referred to are the same as the gilt ones already described with the following exceptions:
Corps of Interpreters—The letters “INT.”
Machine Gun Battalions or Squadrons—The letters “M. G.” in the upper angles of the crossed rifles or sabers.
Corps of Intelligence Police—The letters “I. P.”
Headquarters of Brigades and Higher Units—The letter “H.”
Headquarters of Trains—The letter “T.”
General Recruiting Service—The letters “RS.”
Disciplinary Barracks Guard—The letters “DBG.”
Trench Mortar Organizations—Crossed cannon with the letters “TM” in the upper angle.
Anti-aircraft Artillery—Crossed cannon with the letters “AA” in the upper angle.