The language of Byzantine coins and seals is the same and for much of the history of both it is medieval Greek. The rulers are the same but the seals reflect the vast administrative and ecclesial apparatus of the Byzantine empire. In addition some Byzantine coins have monograms as do many Byzantine seals. Some of these are identifying while some are invocative (Theotokos, have mercy on this your servant). Here is a seal that I will identify for you. One of the three great hierarchs of the Eastern Church is St. Basil the Great (of Caesarea). He came from a patrician background and gave most of his wealth away. He was brother to Gregory of Nyssa and less well known brother to Macrina who became a famous abbess. Basil famously became archbishop of Caesarea. When the Arian emperor Valens sent an official to try and persuade Basil to compromise with Arian views, Basil refused to budge. The prefect said he had never been thus spoken to and Basil said "Perhaps you have never yet had to deal with a bishop." This seal features St. Basil on the obverse. The circle with the A in it stands for O Hagios or Saint and you can see the BA of Basil to the right. The letter above the BA is the final S of O Hagios. The multi-lined inscription on the reverse is [ΘKE BO] | HΘH BAC | ANΘVΠ | [AT]OC. It is an invocative sentence. It means Theotokos (Mother of God) Boethei (come to the aid of) BAC (Basil) ANTHYPATOS. The anthypatos was a proconsul, an office which disappeared after the 11th century thus giving a terminus for the date of this seal which we can safely put in the 11th century. Notice Basil's omophorion, the long wool scarf or stole which is the sign of the bishop. The four dots on it are a representation of an eastern cross which of course has equal vertical and horizontal elements unlike a latin cross which has a longer vertical element. The baldness and other characteristics of the portrait are those of the icons of the time. It is a fixed art and not given to originality.
Interesting seal @Gary Waddingham . I like the way you (or someone) did a bit of history research to date the piece!
These are fascinating, and the one I have (from a group lot) was fun to work on. I still have to finish that work! So cool that you were able to tie yours to a known individual.
I have a seal with St. John Chrysostom and I think I can see a chi on yours in the same place mine is.