Sphragistics is a term that refers to the study of seals or seal impressions. If you're looking for synonyms, there are a few options that might work for you. One possibility is sigillography, which is the study and interpretation of seals and signet rings. Another option is the more general term numismatics, which includes the study of not just seals but also coins and currency. Finally, you might consider using the term epigraphy, which is the study of inscriptions or written symbols, including those found on seals. Regardless of which term you choose, if you're interested in the history and interpretation of these kinds of symbols, there are plenty of fascinating opportunities for research and exploration.