A nice Luger, congratulations.
As far as it being a bring-back or not, I asked a similar question awhile back regarding non-import stamped military Lugers. Ed Tinker advised that lack of an import stamp does not prove it was a bring-back, although it could be. Apparently import stamps were not required until the 1960s on former military pistols.
http://luger.gunboards.com/showthrea...gers-come-from