My first assumption would be that it is a simple good luck charm. However, it could mean a variety of things.
My first initial thought was that it was a personal symbol for a personal use, such as good luck or protection.
However, if you’re going to keep that piece of jewelry, I highly recommend that you cleanse and consecrate it before you start wearing it around, as even if it is a good luck amulet that was personally made by a witch, it could be Enchanted in such a way that it could harm anybody else that wears it.
Which is the reason why if you take a grimoire away from the sorcerer or sorceress, and you try to use it without their permission, I hope you have a good relationship with whatever beings it is you work with, because you’ll probably be meeting them pretty soon.