Seals worked in a similar way to signatures in the ancient world, and were important for proving authenticity, given that written documents were the only reliable method of long distance communication. Most families possessed a seal (they would, of course, need to be literate), and they would stamp a document in order to show who had sent it, and to ensure that it was opened by the correct recipient: a broken seal would reveal that the letter had been tampered before reaching its intended recipient.
Seals came in many forms and sizes: some were made from engraved gemstones, others from ivory or less valuable materials. It is thought that the traditional use of seals derived from Greek and Etruscan origins. During the Roman Empire, use of seals was widespread, and many exquisitely engraved examples survive, bearing depictions of Roman gods or portraits. Often these seals were incorporated into jewellery, such as pendants or rings.
The two imperial busts, depicted in profile, reflect the imperial iconography that was widespread in ancient coinage.