Here is an early Z.F.41 made by Emil Busch A-G in Rathenow (code cxn). The “K.F.” marking (Kältefest) indicates that the scope was lubricated with cold-resistant grease “Invarol”. Early ZF41 sights used flat rollers mounts.
ZF41/1 coded “cxn” for the manufacturer Emil Busch A.-G., Optische Industrie in Rathenow. The “M” marking meaning remains unknown today.