Have you seen this site? The Guitar Vaults offers an online registry for guitars and forum for circulating information about stolen instruments. As TGV describe their services:
Guitar theft is big business and is allowed to thrive in part because, once gone, guitars are very difficult to track down. If (a registered guitar is) lost or stolen, you can let the community know through this site. So, if any instrument should ever come up for sale, potential buyers can search theguitarvaults records and satisfy themselves of the validity of the seller’s claims of ownership.
Read more, watch an introductory video by Dweezil Zappa, or browse the current selection of missing axes at TGV.