[mrerick]

Rust blued pistol barrels were often numbered after assembly and finishing. While the manufacturing process engineering was different at the various manufacturers and in different eras, the process at DWM, Erfurt and Mauser (to 1937) didn't number the barrel until after finishing on most P.08 pistols. There are exceptions.

When the die stamp is driven into the steel metal surface, it causes the metal around the places where the die compresses the steel to stress. This causes stretching and makes the surrounding surface finish more diffuse. This makes the bluing look lighter, and thus like a "halo". Close inspection with a microscope or eye loupe will let you see the effect yourself. There are a couple of photos in the FAQ.