MO in Poland it was the for the Milicja Obywatelska (Citizens Police) In Russian it stood for Ministerstwo Obrony but it also meant the same thing in Polish. Misterstwo Obrony did exist in Poland since 1946 till 1946 it was called the Department of War.
Many theories on the soviet MO markings, but none has been proven or confirmed with proper documentation up to now.
I sold one recently, MO marked Dated 1943/53




























