Stammkp.Gren.Ers.Btl.18 Erkennungsmarke

The tag or 'Erkennungsmarke' shows overall signs of wear. It's broken, but complete and solid. It belonged to a soldier who was drafted in the Stammkompanie Grenadier Ersatz Bataillon 18. This unit was formed in late August 1939 as Infanterie Ersatz Bataillon 18. It trained and supplied soldiers for Infanterie Regiment 18 which was part of the 6.Infanterie-Division. This division saw it's first combat during the invasion of France by crossing Luxembourg and Belgium. From June 1941 on the division saw combat on the eastern front and fought in areas like Witebsk,Rshew, Smolensk, Orel and Gomel. 
In November 1942 the ersatz bataillon was renamed into Grenadier Ersatz Bataillon 18 and in Ocotber 1944 it was absorbed by the 89.Infanterie-Division.  
The 'AB' on both parts of the tag stands for the soldier's bloodtype.
Note the reversed letter 'e' they used as a letter 'a' in the word 'Stamm'.