Tom,
Using a letter between brackets, like the (B) in this example, is usually done in the German language to refer to a state. This basically leaves the states of Baden and Brandenburg as viable suspects. If it was Berlin, they would have omitted the brackets, and possibly added the location within berlin, like N.W. for 'North-West', etc..
This practice of adding an indication of state or other geographic location was done because of the confusion that may result because of the existence of double (or even multiple) names of location in the German empire. We see this in the address references of DWM and Mauser also. Mauser always uses Oberndorf am Neckar in order to differentiate it from Oberndorf in Rheinland-Pfalz and Oberndorf in Tirol.
DWM's Karlsruhe branch always refers to itself as DWM in Karlsruhe, Baden
Ludwig Loewe & Cie and DWM in Berlin always added N.W. to the Berlin name. (Berlin Nord-West).
Anyway, this practice of referring to the state or area in order to avoid confusion makes me believe that the (B) refers to a state or area. Not that it helped much
