Platt, Elizabeth E. “The Signet.” In The Anchor Bible Dictionary, edited by David Noel Freedman, 3:829-30. New York: Doubleday, 1992. [Israel/Kingship/Priesthood]
This is an informative article about the development of the signet ring. It is not particularly well written as an article for a dictionary because she moves around and interjects seemingly extraneous information occasionally. She explains that the signet ring probably came from Egypt as a scarab signet ring which gradually evolved over time. The article also contains a list of the most prominent mentions of a signet ring in the Old Testament with brief but helpful comments about each one. Interestingly, each one was in a position of considerable power.