The Luger collector community puts their faith in the originality of the bluing finish on Imperial Lugers if the serial number stamped on the underside of the barrel exhibits halos/frosting effect around the numbers.
It appears that this same effect is present around the "U.S. NAVY" and "8" overstamp on Colt TSMGs as well as the John H. Barrett inspector cartouche.
U.S. NAVY stamp.JPG 69.92K
22 downloads
JHB Inspector Proof.JPG 128.13K
23 downloads