Alfred, the presence or absence of a halo depends on the model of pistol and the manufacturing process followed at the time. A halo will appear on Imperial Lugers in some places where it does not appear on later Lugers. A careful study of what is expected can be very useful in determining the originality of a finish.
Here is a halo around a Germany export marking on a 1920 alphabet Luger
[The following two images compare a 1918 Imperial P08 to a reblued 1915 Imperial P08. This example is somewhat extreme but immediately shows the differences:
A shot of the reciever halo on the 1918. This is a stamping done after the parts were blued.
The 1914 Mauser was stamped on top of the barrel prior to polishing and bluing; no halo is present, but it is not expected:
Halos may be observed on unblued parts. It is the mechanical polishing that removes the metal distortion that causes a halo.
