Hi Paul
Here are a few of my Reichsbahn bayonets with RBD marking. All these bayoents are "narrow blades" unmarked early bayonets. I only know the RBD 29 with a matching scabbard. The others are in their correct blank scabbards.
RBD 29 is for STUTTGART Direktion
RBD Br is for BRESLAU Direktion
RBD KS is for KASSEL Direktion

Regards
Alain