I found 4 of these last week myself, Adam.
I was delighted - they do not turn up often.
I trip over Caithness decanters but the glasses are never there.
I am suspecting these are Morven, but would love to know for sure myself.
I see these even less often than I see Cannisbay glasses.
One of mine is marked Caithness on the bottom - etched in very big script. 3 have a similar heat smoothed base, with a funny wee mark in the middle which I cannot decide should be there or not. It's vaguely crown, or hand-shaped. It is possibly a tool mark. The other glass has had a flat circular something pressed into the base, to make a shallow well shape.
They all match - and they all
produce an amethyst colour within the brown, when sunlight shines on them - which can make peat coloured ones LOOK amethyst in photos... (which mine did, which is why I've not posted them to ask)