FWIW, that may be an indicator that it was rack stamped in the same era as the gun was made as that was the common font of the day however, the back strap stamp would have been placed by the SFPD or milita and not S&W.
It would also not be unrealistic for a faker (assuming that they knew what they were doing) to use the same style and font as the serial number on the gun to make it look real..
We have seen over the years where attempts at faking have been done by those not so clever and the numbers look nothing alike.