I have a set of German silverware that was standard issue at Ramstein AFB in the 1950's. It is stamped BMF 90. Can anyone tell me what the 90 means? My German mother thinks it means that it is 90% silver, but a German colleague says 900 is means 90% silver. I would like some clarification, as I am unable to find the answer in the place I looked on the net. Danke!