Actually the company was named "Fuess" (not Feuss, which would be a different pronunciation in the German language, ue=ü). The complete name was "R. Fuess, Optische Industrie, Berlin-Steglitz", manufacturer code "cro" (in later times of ww2 only codes were used instead of actual manufacturer names). The code "blc" stood for "Carl Zeiss, Jena, Militärabteilung".