Actually, I thought it was a nice touch. It sounds like he had his family crest reinvented and made into a charm. Seemed to represent his quest to right the wrongs of his family name. I wonder why and when he did this? In other books, his wearing jewelry is never mentioned, not that we're given a chance to read descriptions of him stripping off his shirt very often. OK... wait... let me pause on that thought for just a few seconds more....OK, moving on...
That's another thing -- I noticed in Brimstone, there was much more about how much less Pendergast ended up wearing by the end of the book. He was asked to remove his clothing to be searched and his suit must have gotten shredded to wee bits by the time of the final escape attempt. Are P/C making Agent P into a bit of a tease...?

