Looks like a C inside of a circle (copyright) followed by the word "Vente" or latin for twenty. There appear to be oak leaf designs at both ends of the hallmark. Hope you can figure it out, Sub
Maybe it says R Koven for Rebecca Koven. She's a quality jeweler out of New York City. She has a Linkedin profile, so maybe you could contact her personally.
Without seeing the front/entire piece, and just looking at the maker's mark, I agree with IndianSteve, and think it could be Sarah Coventry. Researching Costume Jewelry Signatures "C"
Breezie