German WW2 Codes
German Optical & Precision Instrument Three Letter Codes 1940
During hostilities, the German Government tried to hide the names of the factories still in production.
They issued every factory with a unique code which was engraved on the instrument
instead of the makers name and location. e.g. Zeiss in Jena used blc and Leitz ( Leica ) beh

Dr Hans Seegar's book Fernglaser und Fernrohre has quite detailed addresses for most of these codes.
ISBN 3-00-000457-2