Final answer:
After selling a car and not purchasing a new one, you should return the license plates to the local DMV. Check with the DMV for specific instructions, as these can vary, and you might be eligible for a registration refund or need to surrender the plates to prevent illegal use.
Step-by-step explanation:
When you sell your car and don't buy another one, you should return your license plates to the local Department of Motor Vehicles (DMV) or equivalent authority in your area. License plate policies vary by state or country, so it is crucial to consult your local DMV for specific instructions. Often, you may receive a refund for any remaining time on your registration or you might be required to surrender the plates to prevent misuse or fraudulent activities.