http://en.wikipedia.org/wiki/Messerschmitt"From this point on Messerschmitt became a favorite of the Nazi party, as much for his designs as his political abilities and the factory location in southern Germany away from the "clumping" of aviation firms on the northern coast. BFW was reconstituted as "Messerschmitt AG" on July 11, 1938, with Willy Messerschmitt as chairman and managing director. The renaming of BFW resulted in the company's RLM designation prefix changing from "Bf" to "Me" for all newer designs that were accepted by the RLM after the acquisition date."
基本上應該是公司改名前是"BF"改名後用"Me".