H.CLEMEN is the maker of this helmet Bruno, the mark is in the rim.I concur, Ed: fantastic markings. One more example that these were usually marked as 92R, and not JR92. It might also bear a reserve stamp. Mine, which is exactly the same as yours, is also marked RJR78 IIB on the other side of the rear flap.
I was not aware that a single maker produced Braunschweig helmets. Thank you, Tony. Which one? Mine has what seems to be a maker stamp in a rectangular frame, inside the shell between plate attachment holes, but I cannot make it out.