The German Identification Tag (1916) is a historical item which can be found by Karl at the occupied casern in Chapter 4.
Location[]
In the area where you collect the soldier outfit, go to the far right to find this item obscured by the table and backpacks.
Description[]
"An identification tag with a detachable part used by the authorities in corpse administration. The main part was left on the body. This model was put in service late 1916."