I’ve had a slight change in perspective on the stamp below. I initially thought it was possibly the initials of the signatories to the document the stamp originally was on, but instead of reading it left to right, try reading it top to bottom. What you potentially end up with is:

R-R-R
WELSH
R-R-R

or:

RIRIR
WELSH
RIRIR

I think it more likely the former given the difference in stroke length between the ones at top and bottom (if they were letters, they would likely be the same height, as that is how we write).

Still no clue as to what it might signify… any thoughts?