I have seen the S51 mark going across the knuckle of the butt instead of the more normal along the butt on a genuine rifle. Genuine because it was still attached to an Army L42! Ironically, I have the original 51 stamps from H&H but couldn't find the letter S. So if he needs the '1' stamp, I'm your man!
Not all Mk3 telescopes have the red W/waterproof or B/Bloomed lens marks. The blooming was easy to remove during normal cleaning and especially when we polished the lenses with jewellers rough polish. When the blooming was removed, we simply rubbed away the letter B. The actual W relates to the type of DRUM. If the drum has a fibre or neoprene O ring between the index plate and the bush, it is a W telescope (supposedly (?) ) waterproof and marked with the red W. But if it has drums without the O ring, then you'd never get it waterproof in a thousand years so it wasn't marked.
The W saga got quite complicated in Malaya/Far East where they ALL had to be waterproof to the extent that even the Mk2's were waterproofed by modifications. The little desiccation screw on a Mk2 was a good indication of its W status and Malaya origins. Does anyone have such a beast?
Maybe this is the sign of another forum article to come....... after the butt thread patching and rectifying the fore-end tie bolt hole.... There's not enough hours in the day.......