The B207 belongs to a very special series of machines believed to have been designated for use at the Führer Hauptquartier (Fuhrer Headquarters). The cipher wheels were specially wired and the wheels and plugboard have markings in red. A total of 24 machines are known to have been produced. A limited number of these machines were further re-wired under extreme security precautions for some unspecified special purpose. To learn more about these special Enigmas, check out this pdf about Hitler's B207.