As a nation state, Italy has emerged only in 1871. Until then the country was politically divided into a large number of independant cities, provinces and islands. The currently available evidences point out to a dominant Etruscan, Greek and Roman cultural influence on today's Italians.
Do you have a foto of the ring? A ring with a design, and or an engraving is not necessary a signet ring.
Generally a signet ring is a "chevaliere", i.e. a ring with a coat of arms of the family. And, it is generally listed, or catalogued?, in a list of noble families, with their coat of arms, either in Italy, or in other countries. Just a simple design may have been something your grandfather liked, or had a special meaning! Like for a school, a club, etc. Aether.
"Fiori di grano.
Amici piu' di prima saremo;
Amici piu' di prima da lontano".