A web site that serves as a database for lost or stolen bikes. This is how it works. When you first buy a bike, it would be registered on the web site with the serial number, make/model, year, and optional photo.
If the bike is ever stolen, the owner will then alert the site, and mark the bike as stolen.
If people want to buy a used bike and want to research the history, they can log on the site and check and see if its been stolen.
Another cool feature would include a sticker placed on the frame, stating that its been registered on a database, also showing the URL of the site.
If someone never bothered to register there bike and had it lost or stolen, they can still alert the site by finding some information, and sending it to the site.
I know it sounds kind of strange, there could be 20 different variations of this.