Y or y was the mark of Sir John Yorke who was at Southwark. It seems pretty conclusive given other marks tie in to specific people at this time. Bow - Sir Martin Bowes, t - William Tyllsworth, TC - Thomas Chamberlayne, WS William Sharrington, while Edmund Peckham (Treasurer) is assigned the ostrich head and G(all coins overmarked) for George Gale at York where coins were never struck, though dies were prepared.