Very nice,
I can tell you how they applied the 'eagle'. It is identical to the eagle marking on the Mauser Parabellum pistols that were sold by Interarms. The eagle was applied by using a template, which was a negative image, printed on bitumen which stuck to a transfer paper. The transfer was applied to the pistol, the bitumen remained. Then, carefully, etching fluid was dabbed across the bitumen template. After enough depth was reached the slide was cleaned/neutralized and the bitumen remains removed, showing the eagle.
I have some of these original templates.