Hylton - Bloodstone was often used for a seal in a gent's ring, so makes perfect sense. The P & G are the maker's mark, the 9 375 indicated the metal content : 9ct gold, the anchor is the Birmingham assay office and the 'u' is the date letter mark. When the date is determined you can then work out the name of the makers P & G.
There is a common misunderstanding about what a hallmark really is. People often confuse hallmarks with makers' marks. A hallmark is nothing more than an indication of metal content, a guarantee of purity or quality, which may include a maker's mark and other marks.
When a piece of jewelry is hallmarked, the marks can help identify the country of origin and, sometimes the date of manufacture, as well as indicate the metal content of the piece.
