John ... sorry ... no idea what/who "JP' stood for.
Possibly the makers initials, but not necessarily.
Back then, silversmiths were not as famous or known as some Pottery artists were.
It also could have been the shop from where it was made.
Many Navajo silversmiths during that period worked out of shops that produced jewelry for certain sellers/trading posts. Your bracelet was never intended to be worn by a Navajo/Indian, but was made for the tourist trade.