Hi and welcome. This is the personal cartouche used by Karel Wunsch (that is why it is a W) during the late sixties, early 1970's when working at Exbor located at the Crystalex complex in the Czech Republic as was Czechoslovakia. This was only used to indicate small run pieces (how many exactly is not currently known but it is safe to assume maybe less than 500). The acid etch was used only when he was overseeing manufacture himself, on designs in small numbers. I do not know if he used this mark after he left Exbor. Pieces I have seen with this mark normally have the Exbor stamp too. But this could have been omitted, i would presume Exbor. It no longer exists and the pattern books are not currently available to the public. Now in his eighties, he still lives and works running a gallery with his wife. A living legend of Czech glass design!