You have a .38 Military & Police (Postwar) manufactured between September 1945 & March 1948. Your gun is considered a transitional model between the Pre war .38 Military & Police Model of 1905 and the Model 10 revolver that is stil available today.
It incorporates the internal hammer block safety introduced in 1944. Hence the S prefix to the serial number. It still has the pre-war long action, which was replaced by the current short action in April 1948. The Model 10 designation was used from 1957 onwards.
Value in very good condition is around $350, there were several million M&Ps in various versions, so they are not scarce.
