It does look very, very Caithnessy indeed, but a bit of a strange one.
If it was a second, (which a wonky lot of base enamels would be in Caithness) why did somebody go to the trouble of facetting and polishing it?
I believe some second-y weights have been found, with inappropriate engraving/sandblasting, because seconds were used for a bit of practice - or simply to make them something non standard, so they could still be sold, but as an unrecognisable/non-catalogued weight, rather than just marking them as seconds.