Depending on how bad the scratches are, ie they're not down to the primer or the bare plastic, go to your local bodyshop supplier and get yourself some 2000 grade sandpaper and some Farecla G3 rubbing compound. Wet the sandpaper in a basin of warm water with some fairy liquid in it, and carefully rub down until the scratches are gone, you won't rip the paint off because the paper is ultra fine, caution should be exercised though, this is known as colour sanding by the way! Then get your farecla and a damp cloth and polish up the paint, it should get a shine back up, then follow up with normal car polish, it should be OK. Be careful though not to break through the clear lacquer that will be on the mirror as you may damage the metallic paint and cause it to shade, when you're sanding the water should be milky, if it starts to become the colour of the paint, you've gone too far. All is not lost though, you just need to apply more clear lacquer if you do this. Best of luck!