I have never seen a Selkirk weight with an impressed mark before, or any other Selkirk glass for that matter. I am quite keen on Selkirk glass and I have seen lots of their weights since I started collecting, but never seen such a mark. I conclude that it must be quite uncommon (and it definitely look like a Selkirk impressed mark as both logo + name look right to me). However, I do not think that it is an early weight as the label indicates end 1980s and the 1990s (not sure after that).
I am afraid I cannot help you more. However someone more knowledgeable is bound to comme across your post soon.
PS: if you plan to sell it, I am your girl...