the intials scratched into the back of the cameo would most likely be the initials of the artist who carved the cameo. Unlike metal that can be stamped at an assay office attributing registered marks to the maker, one of the only ways the artist of a cameo has to claim authorship in shell or harstone is in this comparatively arbitrary fashion.
Even if there were a reliable reference list of the Italian master cameo carver's initials, the most highly sought after signatures would be copied and exploited for profit because it is not difficult to scratch initals into shell as this material is easy to scratch.
I would judge the value of a cameo primarily on the art of the carver and the condition.
