Did patrician families of Rome used something similar to crests?

[Nathan Ross]

would they used it as a symbol on their signet ring?

Wealthy Romans did indeed have signet rings with identifying symbols, used to seal letters, among other things. They could also be used as a sort of guarantee of fidelity - in one recoded anecdote, the late emperor Valentinian III stole a senator's signet ring and used it trick the man's wife into attending the palace alone. The senator (Petronius Maximus) later had the emperor murdered...

However, these rings seem to have identified individuals rather than families, as far as we know, and were perhaps handed down from father to son. The symbols are usually religious or mythological figures, or animals; quite often they were cut into carnelian, and several of these rings survive today.

Roman aristocratic families only seem to have acquired a sort of 'corporate' existence in the later empire. By the 4th century, the networks of senatorial family alliances that had grown throughout the imperial period had matured into something like clans or dynasties. Historians still argue about just how powerful or coherent these 'clans' actually were, but undoubtably families like the Anicii, Ceionii, Symmachi and Nicomachi were incredibly wealthy, owned vast tracts of land and had considerable political influence.

Of course, by then many of these families were Christian, and christian symbols or images would have replaced much of the more traditional ones. However, we still don't know whether these referred to families or to particular individuals. The image below shows a monogram that appears at the top of an ivory panel depicting the deification of Quintus Aurelius Symmachus (a pagan) - it perhaps relates to the Symmachi family.