Jackie — Welcome to the GMB.
It is worth explaining that one of the reasons for the GMB's success is that it has always been ultra careful about respecting intellectual property rights, sometimes erring on the side of caution and safety. If in doubt provide a link, as above.
Re your Webb mark. No. 6 in the series on the great-glass site is the Rembrandt Guild mark, which we now know was in use 1932–37 and possibly a year or two earlier as the 1932 date is from a Kelly's Directory entry (Benson & Hayhurst,
Art Deco to Post Modernism, 2003, p.20). As you can see the Rembrandt Guild mark was a development of the mark on your glass, so your mark must predate the Rembrandt Guild mark. Also I have recently bought a Webb piece carrying the same mark as your glass which appears to have been made around 1927, taking the mark back a little further in time if I'm correct, and matching the introduction of such marks at Stuart, Tudor, Walsh, and E&L.
I hope that helps,
Bernard C.
