Your question sure threw me for a loop. I had no idea that mark would be there, but I looked and sure enough, it is, on the front strap about 4mm from the bottom. It is like the one on the "Siamese Mauser" except that it is smaller, about 6mm diameter.
I doubt a Clement was used by any military service, but maybe Siamese police?
Good luck in your research and glad to have been of help.
BTW, I have understood that the 5mm pistol was called the Model 1903 and the 6.35mm was called the Model 1908, though they were otherwise identical, and numbered in the same series. Does anyone know for sure?