Hi Ron
I have no proof positive on these but have had a number of them over the years. Recently a friend of ours bought a collection and in the pile was an ersatz bayonet with one of these on the sheet metal scabbard. It fit quite well. They tend to be too wide for an S84/98 bayonet and not wide enough for a S98/05. I've kicked around the idea of perhaps a Turkish or Bulgarian contract frog. I would like to say that all I have seen similar to these are marked Berlin 1917.
Larry