Lenstag (https://www.lenstag.com/) is a new site aimed at discouraging the sale of stolen camera gear and helping the original owner locate the gear through tips. And another great thing about it - it's free!
From Lenstag's FAQ:
How does it work?
Lenstag works like this:
Bonus feature: if you sell or give an item to someone else, you can transfer the record to them using Lenstag and save the next person from having to re-verify.
How can I tell if a camera or lens is stolen?
Do a web search for 'stolen', the serial number of the item and 'lenstag' for good measure. If the item's page shows up, there's a good chance it's stolen. If you know something about the item (location, craigslist post, etc.) please type it into the box and leave your email address (optional) so we can follow up.
Check out the Lenstag website for more information.