The "SP" mark on vintage Avon jewelry generally stands for Silver Plate or Silver Plated, which indicates the base metal has a thin layer of silver applied over it.

Even though this specific necklace has a warm, yellow-gold look, Avon frequently stamped their jewelry with universal factory codes or base metal identifiers. An active listing for this exact piece can be found on "Vintage Avon Turquoise Flower Necklace Gold Tone 19”". Lovely necklace it's delicate enough to stack with another necklace for a cool look. Or a beauty on its own. No condition issues.