sorry Sue, appreciate your mark is there, but too feint to see with certainty, and might benefit from a black background and the use of antiquerose's magnifying glass.
Would agree with Patricia re Reynolds book which is most definitely worth having if your area includes JWW material - my only personal gripe would be that reproductions of the patterns are not the best of quality images and most of the writing is at best difficult to read - but I guess better to have than not. I have three pieces only, two of which are marked - one being the little Pompeian u. posy vase on plate 21 and a nice pair of drinking glasses that I picked up this morning, and as yet am unable to locate in the patterns. I saw the posy vase again this morning, and although I spent ages looking couldn't find a mark. My third is a large Pompeian bowl which defies me to find a mark, and although you can't make assumptions remotely from three pieces, just maybe (I'm thinking) the earlier material is more poorly back stamped.
The mark shown is quoted by Reynolds as 'c.1930 - 1951', but as is common with many of the glass backstamps, does appear in various publications.