Aha. Well, an importer mark was about the only remaining explanation.

You didn’t give your gun’s serial, but if it falls into the same time frame as the gun whose letter you posted, it originally shipped in polished blue commercial finish. Your photo looks like it was parkerized over the stamp. So the Austrian police marking may have fallen victim to the refinish. Or this was simply a revolver that remained in Austria after the British withdrew because it was lost, stolen, or disposed of in some other way.

The revolvers that the BPC purchased ended up in Britain and all over the former Empire, in Canada, Australia, India, Africa. Why Roy mentions Turkey of all places, which was a neutral country in 1941 and through most of the war, is a mystery to me.