I thought someroso referred to more than one colour.
These are really quite common up here, though marked is a bit unusual. They come in several colours, clear, neodynum, amber (a nice rosy kind of shade), amethyst, smoke and green (off the top of my head). They can sometimes be difficult to tell from the WFs ones - and I've been told by a WFs person that they can't always tell them apart either. (I offered some as part of my bit for the mould fund, but they were declined because of this. They went back to the charity shop where I found them)
Strathearn did clear ones as well, but they tend to have a "pointy" shape of colour in the base.
Sometimes they're tall like this one, but (particularly the neodynum ones) are a bit fatter.
If the base is a bit concave, moulded rather than polished flat, you should suspect Caithness.
Sorry, can't help with the date - have you trawled Frank's site, "Scotland's Glass" yet?