Make sure the pw is at room temperature, and have some water on a flattish saucer also at room temp, try soaking it.
If that softens the glue, but doesn't actually get it off, you can try, very gently, with a razor blade or scalpel - being careful to keep the blade almost flat against the surface of the glass.
Failing that, try some biological washing liquid in the water, soak, repeat the blade technique.
If all water-based methods fail, you can start on things like nail-polish remover.
Christine's right, though, it should have Caithness and the name of the design etched onto the base.