Lenstag is a user driven database of serial numbers and their corresponding camera/lens/flash/whatevers, verified ownership via user uploaded photos. You can flag your gear if it goes missing, and you can look up a piece of used gear before purchase to see if it was stolen or not. If you sell your gear, you can even transfer ownership. New features are being added all the time. Maybe it won't cut down theft, but it will prevent you from purchasing stolen property.
If you had any doubts about the effectiveness of this type of thing, Lenstag celebrates it's first recovery today. Philip Martin, who is being heralded as the most ethical man of the moment, recently bought several pieces of camera gear from a stranger on craigslist.org, unfortunately, Mr. Martin did not check Lenstag before purchase, but DID return the stolen gear AFTER purchase and realizing that he had bought stolen goods.
Taking the high road and returning stolen goods feels great, you become someone's hero, but by downloading the free Lenstag app, registering your gear, and checking the serial numbers of potential purchases for flags, you can be a hero AND save yourself the potential losses of possessing stolen property.
Please visit the homepage of Philip Martin, Lenstag, and read the first story about the success of Lenstag here.