I've wondered about the mark, too. As mentioned before, it is like the mark for Barovier-Seguso-Ferro (BSF), a company in Murano in the 1930s that became Seguso Vetri d'Arte in 1937. I've wondered if they may have been involved in the marketing of the things that have the symbol. My thinking is probably naive, and going way beyond in inference -- much based on Seguso VdA managing Salviati. The companies did so much more than we are often aware of. I haven't been able to find anything about BSF beyond their glassmaking, but there were people who had connections in England, Czechoslovakia, and France. Who knows?