Hello Pete,
I have the same markings in a 1916 holster, that was my own for years and I didn�´t realize it!
it is: Rudolf Wiemer&Co. M�¼lheim-Ruhr, which is near to D�¼sseldorf.
M�¼lheim an der Ruhr map:http://www.map24.de/map24/routing.php3?map24_sid=7457a71c3402ad25554af1c8eb649410&newroute=1&map24 _sid=7457a71c3402ad25554af1c8eb649410&sstreet=Stra%DFe&szip=PLZ&scity=d% FCssel dorf&scountry=de&dstreet=Stra%DFe&dzip=PLZ&dcity=m%FClheim+ruhr&dcountry =de&rtype=fast&desctype=standard&loadlimiter=&usecity=&maptype=JAVA&mid= MAP24&x=68&y=11