thanks for the size - hopefully it might help.

Identifying cut patterns on clear drinking glasses is notoriously difficult - partly because there are many thousands of designs - if you look at the main States web site - Replacements, Ltd. - you'll see ...... and partly because of the lack of available manufacturers catalogues/images. Obviously some are more common than others, but given the vast number of different designs, it can be an up-hill task, although you do at least know the maker, which reduces the possibilities.
Most backstamps - yours included - are applied mechanically, so would not be described as a 'signature' - and would be correctly referred to as a backstamp. A 'signature' would be applied by hand, literally, and some glass does have just that ..... the designers name applied by hand with a stylus or diamond point.
Not sure what size wine glass you're accustomed to using, but I'd have thought 5.5" probably about normal, although I appreciate these things have developed larger capacity bowls over the past 20 - 30 years. Bearing in mind the historic proliferation of different shaped bowls for an equal variety of alcoholic drinks, then always possibly yours might be for something other than plain wine.
Royal Brierley was a name change that replaced the earlier and older company name of Stevens & Williams, and was a change that occurred sometime in the early 1930's. In terms of recent production - i.e. the 1990's - something like a fifth of R.B.'s output was exported - mainly to the States and Japan, so there should presumably be a fair amount on your side of the pond.
Yours is an attractive glass, hope you find some more of the same pattern, and best of luck in your search for a name.