IR Reflective film has been reliable for IFF protection since WWII

IR (infrared) reflective film is probably the most popular and well known identification film used in military and law enforcement operations today.  Since its inception in WWII, IR reflective film effectively marks personnel primarily in the form of patches worn on the helmet, chest, and shoulders.

The IR Film is seen only when illuminated with a Night Vision device (NOD,NVG).  When white light hits the patch, it is absorbed by the coating and the user remains undetected.  Soldiers and police can successfully move about in a stealth position and remain protected from friendly fire.

The above image shows the patch under normal light (left) and as veiwed with a night vision device (right).