Finger Rings including Signet Ring History by: Anonymous
This is not the hallmark. Signets rings are engraved with arms, shields, legends and various other devices. It could also be an engraving in intaglio of a family crest.
An interesting book with all kinds of information on finger rings through history is the "Catalogue on Finger rings, early christian, byzantine, teutonic, mediaeval and later" and can be found in the Jewelry Resources.