I loved this piece the minute I saw it! It is a gracefully designed initial "W"...probably the loveliest way I've ever seen an initial pin done. (I almost kept it...if you turn it upside down it COULD be an "M"...one of my initials, but it might not quite hang right!) My loss...your treasure!
It is marked 925 and Made in Mexico plus the eagle mark 4. This seems to be the generic mark used for Taxco and Guadalajura. One reference book also says the mark stands for FCHH & JGN. It measures 1-1/2" x 1-1/4". It's in excellent condition although the hallmarks are a bit worn.
I finally located one vintage jewelry shop that has a "C"...wouldn't it be wonderful if your name needed both?
This is a lovely, lovely piece.