Dwight and Jim,
Keen observations about the "swastika" in the proof. 1928 rules out the "Hakenkreuz" or Nazi swastika, and Dwight's notice of the horizontal and vertical arms of the cross might lead me to believe this was actually a form of the early chemical symbol for crucible.
Although I have no idea what relevance this would have to an Army Quartermaster, it is more plausable (I think) than a Nazi swastika in 1928. If the mark on the topic Luger is original and not a later day "Waffenfabrik USA" addition, I guess that leads to the conclusion that the line drawing in Costanzo was made by someone who did not closely evaluate the mark and assumed it was a swastika.
Although it has its flaws, I have to agree with policeluger that Costanzo is a great reference, and considering when it was compiled it is the opus magnum of Luger proof marks