There was also a Bulgarian lion proof on the right side of the receiver, but that likely has also been removed.
Prior to WWI, Germany's DWM (Deutsche Waffen-und Munitions Fabriken) was the lone manufacturer of Lugers (where they were known as Parabellum pistols, Luger is an American nickname). The Swiss military was the first country to officially adopt the Parabellum, in 1900, and DWM didn't sell to the German military until 1904 (I believe the Navy was the first to adopt it). In addition, DWM engaged in contracts with other countries, one of those being Bulgaria, who were shipped three separate contracts - in 1903 (1,000 Old Model 1900 Lugers in 7.65mm), 1908 (600-800 New Model 1906 Lugers in 7.65mm) and 1910-11 (~"10,000" Model 1908 Lugers in 9mm). The exact numbers shipped are still in some doubt as the original records were destroyed and we only have the guns and their serial numbers to guide us today. The 1900 and 1906 Model Bulgarians had beautiful chamber crest stamps, but it's the Model 1908 that had the most unique features, including the Cyrillic characters, the lanyard loop, the displaced DWM logo on the chamber, etc.
The early contract Lugers are a fascinating study, and are my primary area of interest (especially the Bulgarian contracts). The 1908 Bulgarians, manufactured in 9mm Luger, were used in the two Balkan wars of 1912-13 as well as WWI and WWII (those that survived). The earlier models were also used and were often rebarreled to 9mm as well. Most likely, all of the Bulgarian Lugers were issued to officers as sidearms. Seeing as much action as they did, they were used hard and were often refurbished and rebarreled, and Bulgarian Lugers in excellent original condition are extremely rare (such as, you can count them on one or two hands). Like I said, those that survived WWII were in such bad shape that they were mostly parted out and you can find Bulgarian frames, receivers and extractors scattered all over the place wherever needed to make a shooter functional again. I've even seen guns that consisted of a 1908 Bulgarian frame and a 1906 Bulgarian receiver.
By the way, lugerforum.com is also an excellent forum and resource and shares many members with luger.gunboards.com.