St.kp.Füs.Ers.Btl.39 Erkennungsmarke

The tag shows overall normal signs of wear. It belonged to a soldier who served within the Stammkompanie Füsilier Ersatz Bataillon 39. This bataillon was formed in August 1939 in Dusseldorf as Infanterie Ersatz Bataillon 39. It trained and supplied soldiers for Infanterie Regiment 39 which was part of the 26.Infanterie-Division. This division (and her units) saw combat during the invasion of Belgium, France and later in Russia. It fought in areas like Rshew, Donbogen, Kursk, Smolensk and Kowel. After the division was destroyed in the summer of 1944 in the area of Cholm the remains were used to form the 26.Volks-Grenadier-Division. This division was put into action during the Ardennes Offensive in late 1944 and early 1945.

The Infanterie Ersatz Bataillon became Grenadier Ersatz Bataillon in October 1942 and from December 1942 it was renamed Füsilier Ersatz Bataillon 39. 
From the beginning of 1944 the bataillon trained and supplied soldiers for units within the 264.Infanterie-Division.

A Stammkompanie was a unit that trained the soldiers. Often the soldiers of this kompanie 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.
The 'O' on both parts of the tag stand for the soldier's bloodtype.  

A Füsilier marked/related erkennungsmarke is not so easy to find.