Hi Norman,
Looks like ZBS - Zelezny Brod - and the oval blue label appears to back this up. One designer most commonly associated with this is Miloslav Klinger, but there were others and some shapes have not had a designer attributed yet. Perhaps Jindrich may know.
As I am sure you know, this appears to be Alexandrit/Neodymium glass, which changes colour from an icey blue to a pleasing violet/purple depending on the type of light.
The label may help to date it to a period - MADE IN CZECHOSLOVAKIA or MADE IN CZECH REPUBLIC....as many of these were made for long periods, or reintroduced in the 1980s-90s.
Mark