Your bike has been stolen? You found a bike or you have a suspicious offer to buy?
If a bike turns out to be missed, "Radklau.org" can help to establish contact between the finder and the person who submitted the advert. This site may help to return lost bikes to their legal owners. As a side effect, thiefs are forced to modify stolen bikes in order to reduce the risk of a recognition, which makes their "business" less attractive.
Finally, the site may help to identify bike-thievery hotspots.