Brassard

Brassard: A brassard is an armband used to display a military insignia. The brassard might be used for a temporary insignia, such as Officer of the Day, or part of the uniform.

Three of them were armed and wearing brassards on their sleeves, making Castillo think they were probably the AOD, the FOD, and OD, which translated to mean ... and the Officer of the Day.

Quotation from: