bvu is the manufacturer's code for "Kuhlman, Franz, Werkstatten fur Prazisionsmechanik u. Maschinenbau, Hauptwerke Wilhelmshaven." This info from "Liste der Fertingskennzeichen fur Waffen, Munition und Gerat" published by OKH Wa Z 2 in 1940 and reprinted by Karl R. Pawlas, Nurnberg in 1977 as ISBN 3 - 88088 - 214 - 2.
Additionally the markings Z.m.P. could have been those of the soldier's unit, as some units stamped their equipment upon it reaching the armory.
But I am actuaklly wondering, you said you're in a museum and there is a museum in Prague that I visited dedicated to the history of the Jews, particularly the holocaust. The museum is called the "Zidovske Museum V Praze", their initials are Z.M.P., is it possible you have come by an old article of theirs, as some museums, (including the one I curate for in Ontario) do stamp their articles.
In fact we have two canvas bags from Canadian troops in WW2 that are probably almost identical to yours despite the difference in countries of origin, and we have HMMH stamped on the front, (why they stamped the front I don't know, I feel it takes away from the genuine article, but they did that before I ever got here); The fact that the stamp is there seems to always be more of a question maker than, as people are always trying to find a regiment of Canada that has the initials HMMH and when they can't they ask the staff. Thats when we tell them it means "Hamilton Museum of Military History". Your bag could possibly be the same deal.
You can find the museums website here
http://www.jewishmuseum.cz
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