In Charles Hajdamach's British Glass 1800-1914 I could not find that mark either under Stevens and Williams marks or under Fakes and Forgeries.
In The Crystal Years, the book about Stevens and Williams there was no record of any marks. Just for future reference, not that it definitely precludes your vases being made by S&W, there were no pieces that bore any resemblance to your vases in this book either.
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