No thats the weapon number.
Bz.15.285 is weapon number 285 (could be rifle, pistol, or bayonet).
Below are some representative Reichsbahn unit marks as found on bayonets:
84/98 N SBR 125 Blued Saarbrucken Railway district
S84/98 N SBR 296 Blued Saarbrucken Railway district
S84/98 N BZ11 Blued Frankfurt Railway am Main district
S84/98 N Bz.15.217 In-The-White Köln Railway district
S84/98 N Bz.15.277 Blued Köln Railway district
S84/98 N R.B.D.29 Blued Reichsbahn Stuttgart district
S84/98 N RBD KS 172 Blued Reichsbahn Kassel district
S84/98 N RBD KS 722 Blued Reichsbahn Kassel district
S84/98 HC BZ11 E&F Hörster (Commercial) Reichsbahn Frankfurt am Main
S84/98 HC RBD KS 186 E&F Hörster (Commercial) Reichsbahn Kassel district
S84/98 HC RBD KS 209 E&F Hörster (Commercial) Reichsbahn Kassel district