This image was cropped from a larger photo titled, "Bringing aboard wounded at Boreeaux, France". The officer in charge and the enlisted litter bearers, all of whom are transporting wounded Doughboys onto a American hospital ship, are all wearing unidentified brassards.
The officer's brassard appears to be white with a dark horizontal stripe bisecting it. Initially, I thought the enlisted men's brassards were Red Cross brassards, but there is no evidence of a red cross at all. Therfore, the single color brassards must have been designed for a different purpose.
Any guesses as to what either of these unidentified brassards represent?