The standard service M&P came with fixed sights. At the time yours sold, probably ca. mid-1947, there were no target model (adjustable sight) M&Ps being made, as there were in the pre-WWII period. Excepting the very few and very desirable Mexican Model target revolvers made in 1946 in the SN range between S812000 and S817000. The K-38 replaced the .38 Special target model M&Ps around early 1947. They all had K-prefix SNs.