The initials H.S are the maker's mark. There are two British makers with very similar H.S initial marks-
1. Harriet Samuel (1880s-1970s) 2. Henry Stratford, Ltd (Silversmiths & Retailers, Sheffield, UK) (1880s - 1920s)
The letter Y at the end of the series is the date mark. By cross referencing the date letter on the ring with the date letter year charts you can determine the year of assay. The date letter charts for the UK assay offices can be found at Researching British Hallmarks. The date letter charts appear on the top right hand corner of the page when you open the assay offices page accessed by clicking on the link above provided. You have to be meticulous with date letters - the typography must all match.
It would be interesting to know what the symbol is next to the hallmark (18)? This could also help to narrow down the date.
