Very nice zind id tag (erkennungsmarke) from a member of the 4./XVI. Festungs-Infanterie-Bataillon 999, which was a penal unit (Bewährungseinheit).
The XVI. Fest.Inf.Btl. 999 was stationed on the Greek island of Lemnos, but the owner must have been transferred to another unit, since this tag was found near Priekule (Preekuln) in Kurland, Latvia.
Extremely rare tag to find and in very good condition.