St.Kp./Grz.Inf.Ers.Btl.125 Erkennungsmarke

The tag or 'Erkennungsmarke' shows signs of wear. The soldier of the tag served within the Stammkompanie Grenz Infanterie Ersatz Bataillon 125. The bataillon was formed in August 1939 in Idar-Oberstein. In Dezember 1939 the bataillon was used to form the II.Bataillon Infanterie Regiment 332 which was part of the 197.Infanterie-Division. The bataillon was reformed and from 1940 it trained and delivered soldier for different Infanterie Regiments, Grenadier Regiments, Festungs Regiments and and some other units. 
The 'O' on both parts of the tag stands for the soldiers bloodtype. 
A Stammkompanie was a unit that trained the soldiers. Often the soldiers of this company were soldiers who had frontline experience and/or where no longer fully usable on the front due to injuries. Of course this changed later in the war and they also where put into action as there was a shortage of (front)soldiers.