Hello Apostolos,
I think Dwight asked about the type of surface on the thumb safety lever to help identify what might be one yours, type 1, 2, or 3...see these photos to show more :
The Swiss luger production was the first contract delivery DWM made in the early 1900's. All of these Swiss luger had numerous little Swiss cross "proof" marks stamped on gun parts, including the left side of the barrel. Some other M1900 luger (such as commerical and AE) have appeared with barrels with the Swiss cross marking. This implies that some barrels were extra and left over and used on other contract lugers (and so possibly, your Bulgarian...).
Here is a photo of the Swiss cross on the left side of a luger barrel :
Regards,
Pete... <img border="0" alt="[typing]" title="" src="graemlins/yltype.gif" />