From The Grey House:
The woman wore a silver chain with a large red stone. The stone was set in silver backing and had silver markings on it. To a casual observer, the markings probably looked like a random design. Natalia had seen a large picture of it in the Slayer journals and knew better. The one she found in the book was the one Vincent worn. That one had a fleur-de-lis that wrapped to the edge of the stone. This one had a paw prints behind a silver fleur-de-lis. Natalia had a vague idea what the design meant but as the red stone was the exact color of the necklace Vincent wore, Natalia could surmise only one thing. The woman worked for Vincent.