I have recently seen that label on a few different pieces.
Seen it on some Barbini pieces from the 60-70s, on Cenedese pieces, G.F. pieces, Venini, and even Barovier pieces... I think its part of an import label/or specific company that sent the pieces out. It doesnt seen to be of any particular glass house (Barbini, etc.). I think if you follow the letters on the side, it could correspond to a year?
I have tried to look into that, but its really hard to find out, specially since some designs cross over from the 50-60-70s. Also the labels might have been put there years after the items were made, like sometimes happens, things get stored and resold at later times by a gallery, etc.