Way to large to use as a license plate topper.
It's original purpose is probably long forgotten, but it looks like it may have been for a mail box, a fence or a railing decoration.
Weather vains are usually made out of copper, and develop a patina over time, they do not rust.
It's not carved, and I can't tell if it is antique or not, as it doesn't take long for bare metal to age when out in the weather.
