The fact that your gun is a .38 Special and has a 6 1/2 barrel and adjustable sights narrows it down to being a Military & Police Target revolver built before 1910. Does the caliber marking include U S Service Cartridge too? That marking disappeared a bit before the 6 1/2' Barrel did so the prior estimate of 1908 is in the ballpark.
And, BTW, CTG. is the abbreviation for Cartridge. It is nor part of the model name. Until ca. 1957 when model numbers were added to the description of models all S&Ws fell under the general classification of "Named Models", where the model name was the only descriptor. In the case of your gun it would be a .38 Hand Ejector, model of 1902 or 1905, depending on some specific features that distinguished them, which most would not have known at the time.