Gents,
I'm pretty sure the old stamping was an S/42. Some rotating and enhancing of the image shows the faint outlines of the S and the 2.
Ã?? as well as Ã??b are both acceptable abbreviations for the word Ã??bung (practice, test).
Removing the original manufacturer's logo would help in identifying the pistol as 'messed with' and would therefore protect the original producer against possible liability issues if the 'test pistol' would fail.