Danish motorcyclist helmet, certainly. Of course I had no idea at all before Mark posted his latest set of pics, but the inscription was an obvious clue and I can now pass on a bit more info from Anders Skotte's useful little book COLLECTORS GUIDE TO SCANDINAVIAN MILITARY HELMETS VOL. 1 - DENMARK AND NORWAY (alas Vol 2 has yet to appear...and maybe never will). It is shown as the Danish-made M55 Despatch Riders helmet, the shell being plastic, originally white but later painted green. It appears that it is designed to fit - in the same way as a liner - into the Danish M48 (M1 clone) shell, for further protection as appropriate. " Forsvarets Ejendom" is 'Government Property' - or 'Armed Forces Property' more precisely, I think, and is not a makers mark.

Pretty unusual object, really, don't think I have ever seen one before.