Gas Brassards were issued to all American, Canadian, British and Allied troops involved in the D-day Landings- both infantry and paratroopers. They were designed to change color in the presence of chemical agents in the event that the Germans resorted to using gas to defend their lines.
To wear, simply slide it up the arm of the outer garment, and fasten the epaulet through the loop. These were copied directly from an original for dimensions.
Original brassards were made of coated paper. For durability purpose, this reproduction is made of coated fabric, but looks exactly the same.