I beleive the badge you have is from the Baltic States area due to the construction of the badge. Thin silver stamped. The enamel color blue is often found in Lithuanian badges. I would start there in your research. The top row of letters "3.X.D." stands for "3rd Railrod Detachment". The bottom row letters "C.K." identify the Rail line. My geuss is "Samositia - Kaunus". Samositia is Central Lithuania and Kaunus was the established capitol of Lithuania in 1918. Bermont-Avalov liberated much of this area from the Bolshaviks in 1918. This is an educated guess, but I would start here do to how the badge is constructed, color, date, and letters on it. Quick note : Some Insignia found in 1918 were made from melted down coins, thus the silver and gold availability. Probably reserved for officers.