That looks like a 5 stamped over something to me.
In the other thread you posted in, sodacan posted a pic of a 1950 and a 1955 together here-
http://smith-wessonforum.com/141257290-post18.html
Maybe he will post that pic here.
The 1950 guns that have lightweight barrels have beveled corners on the top front edge of the frame. Heavy barrel guns do not have those bevels. Your frame is not beveled, so it was never a 1950 Model. It is a Model 25.