Yeah, Gentlemen, I think, or better I am sure I have the clue now!! I could not stop thinking about it all the day long...
Because this marking is on a Unteroffizier Baden M95 Haube, I was sure it must have something to do with the Herzogtum Baden. As a child, I was a few time in Baden-Württemberg for vacations with my parents (I still love this Schwarzwald-country)and I have visited in the past a few towns there. Today evening I suddenly had the thought!!
The regimental marking means the Baden town of DONAUESCHINGEN !! Yes, that´s it! Then I searched a little on the internet and it was easy. Look at this:
B(ahnhof).K(ommandantur). D(onau)esch(in)g(en)
Yes, the particular railway station of Donaueschingen was always a very strategic place because of its traffic knot point of 4 railway directions!! This particular helmet was first worn at the IR 142 and then by a member of the Baden Bahn-Gendarmerie. ALLES KLAR JETZT!!
Philippe