Hi,
There is a decent chance that the engraving on the navy is German in origin, but I'd expect it to be some GI's idea of a joke, engraved by a liberated engraver in search for some hard cash.
It having been property of Hermann is just as likely as his Vermeer being genuine...
A similar looking engraved Navy as discussed on Jan's website:
http://www.gunboards.com/luger/uploa...uger1916_3.JPG