I looked at what must have a M&P of some vintage this afternoon. "K" frame size, 6" barrel. S/N was a straight 6 digit, no prefix (15xxxx IIRC). There was no address line at all, only the Smith & Wesson logo. No markings on the right side of the barrel. Patent dates and such on top (sorry, I don't remember which ones.) and s&W 38 special on the left side of the barrel. The ejector rod had sort of a bulge on the end, sort of knurled knob. Under the cylinder release on the left side, there was a pin, but no matching pin on the right size. Five screws in the sideplate.
It was simply marked a "Pre Model 10."
It was simply marked a "Pre Model 10."