There are several reasons why you may have old license plates. Maybe you bought a new vehicle and didn't transfer the plates from your old vehicle. Or maybe you donated your vehicle to charity or sold it to a junkyard. Whatever the reason, the Department of Motor Vehicle (DMV) has a few general recommendations on how you can decimate them so they can't be reused.
Remove or deface the month and year stickers on the old license plates (if applicable). Use a sharp pocket knife to scrape the stickers off. If you can't completely remove them, use the tip of the knife to scrape through them so they're no longer readable.
Use a permanent marker to cover up the numbers/letters on the license plates. With the stickers defaced and the numbers/letters illegible, the plates can't be stolen and used illegally.
Cut the old license plates up with a pair of tin snips if you haven't already defaced the stickers and numbers/letters. Be sure to cut the plates so they are no longer usable.
After old license plates are destroyed, you may be able to return them to your DMV to be recycled. Since 2004, license plates have been made out of recycled aluminum. Prior to that, license plates were made of galvanized steel, another recyclable metal.
Be careful when cutting old license plates or handling plates with rough edges.