Vinyl on vinyl can be difficult to remove, as the two have likely fused together to form one. I have a few things to try, but I can't guarantee success, unfortunately. I would start with baking soda, and use it as you would an abrasive cleanser, and scrub. Non-gel toothpaste may also do the trick. If that doesn't work, try mineral spirits (available at most hardware or department stores), and as a last resort, I would try rubbing the stain with silver polish. Be sure to rinse thoroughly after trying each product.