Yes, in Washington State, you generally need to return your license plates when you cancel your vehicle registration or when you sell or transfer your vehicle.
Call the Department of Licensing at (360) 902-3770, visit their Department's web site (dol.wa), or contact your local auto licensing office. I have sold or transferred my car.
No, in the state of Washington, it is not required that drivers return their license plates after selling their car. If you do want to return your plates, you may be eligible to get a refund if the plates are not expired.
While you can keep old license plates as mementos (if you remove or invalidate the tabs and do not display them on a vehicle), you can also dispose of them.
How to Sell a Car in Washington Step 1: Allow the Buyer to Have the Car Inspected by a Third Party. Step 2: Clean Out the Vehicle. Step 3: Remove the License Plates. Step 4: Complete a Bill of Sale. Step 5: Collect Payment from the Seller. Step 6: Sign the Title to Formally Transfer Ownership. Step 7: File a Report of Sale.
Anytime you sell a vehicle in Washington, you should report the sale to the DOL and remove the plates from the vehicle. By removing the plates you force the new owner to transfer the title and register the vehicle. The plates are registered to you for the vehicle--they do not belong to the vehicle.