"I have a small 9 carat amethyst gold ring with the hallmark CL & S in the first stamp, the numbers 375 between two marks that look like an upside down V with an extra leg in the second stamp, 375 boldly stamped, then the last stamp could almost be a castle in a square stamp with the corners cut off. "
OK. The upside down V with an extra leg will be the Birmingham assay mark. It is an anchor :-)
The ring is marked 375 with a decimal stamp for 9 ct gold, this tells us that the ring was made around the 1930s. This is when carat markings were replaced in the UK with decimal values.
CL&S in an oval is the maker's mark for: Charles Lyster & Son (Birmingham, UK) - ca 1890s - 1930s
