Stamkp/Pz.Gren.Ers. Btl.108 Erkennungsmarke

The tag or 'Erkennungsmarke' shows signs of wear. The bataillon was formed in December 1940 as Schützen Ersatz Bataillon 108 in dresden. This bataillon trained and supplied soldiers for Schützen Regiment 103 & 108 which was part of the 14.Panzer-Division.  This division and her units saw action in Yugolavia and after that it participated in the invasion of Russia. It fought in areas like Don, Mius and Stalingrad. 
In July 1942 the bataillon was renamed Panzer Grenadier Ersatz Bataillon 108 and it still supplied soldier for the, by then renamed, Panzergrenadier Regiment 103 & 108. 

A Stammkompanie was a unit that trained the soldiers. Often the soldier of this kompanie were soldiers who had frontline experience, but no longer were fully usable at the front due to injuries. Of course this changed later in the war as there was a shortage of (front)soldiers and where mobilized also (as can be read above).
The 'A' on both parts of the tag stands for the soldier's bloodype.