Originally Posted by FirstInFlight

Your car has a license plate number - similar to an FAA registration number. Both cars and planes also have serial numbers (engines are also numbered as were propeller blades at least at one tine). But if your car is a company owned vehicle it likely also has a fleet number. And like cars, you can swap FAA registration numbers if you so desire. The FAA cares about N numbers, the manufacturer cares about airframe numbers and the airline cares about fleet numbers