This is an ingenious idea that we hope takes off. Lenstag, available for iOS and Android, is a system for preventing the resale of stolen cameras, lenses and video equipment.
Once you sign up, you register your camera kit using the serial numbers, then verify that you own the gear by uploading a photo of the serial number or something else that demonstrates ownership, like the warranty card. If you sell the gear on, you can transfer this verification to another user to save them having to re-verify.
If your kit is stolen, you can notify Lenstag and the app will create a dedicated page to alert other buyers not to purchase the item. If you're looking to buy a camera or lens and are doubtful about the seller, you can search for it on Lenstag and see if this kind of page appears: