The Fob and Seal that was presumably JLD Mason's has been a mystery both as to origin and meaning.

Did he buy it or receive it as a gift?  Was it a family item given to him?  Would it have been from the Masons, Delaneys, Egans, Eastaffs???

In doing some research to come up with what the symbol is, my best guess currently is that it might be the goddess Athena/Minerva.  The following quote describes the goddess and mentions not only that she was the goddess of war but also the goddess of physicians....

Minerva 
The Roman goddess of wisdom, medicine, the arts, dyeing, science and trade, but also of war. As Minerva Medica she is the patroness of physicians. She is the daughter of Jupiter. In the temple on the Capitoline Hill she was worshipped together with Jupiter and Juno, with whom she formed a powerful triad of gods. Another temple of her was located on the Aventine Hill. The church of Santa Maria sopra Minerva is built on one of her temples. Every year from March 19 - 23 the Quinquatria was held, the primary Minerva-festival. This festival was mainly celebrated by artisans but also by students. On June 13 the minor Quinquatrus was observed. 
Minerva is believed to be the inventor of numbers and musical instruments. She is thought to be of Etruscan origin, as the goddess Menrva or Menerva. Later she was equated with the Greek Athena. 


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In IE mythology Minerva's multi-faceted skills recall the great Celtic goddess Brigantia/ Brigit, who also knew medicine, the arts, learning, and had some warrior functions. Even so, Minerva seems to have been of Etruscan origin, where she was found as Menrva. Menerva, Minerefa, or Minerifa. Indeed, one of her earliest temples in Rome was on the Mons Caelis, where tradition had Etruscan allies of the legendary Romulus stationed. Roman tradition also had Numa bringing Minerva into the Roman pantheon.