Usually GPS comes with some kind of number which distinct each device. If the owner of the device have noted that number then that number could be used to report filing missing GPS. HOwever if that number hasnt been recorded by owner and he lost GPS, its almost impossible to track the device. In general and in most cases people dont record that number and ths when they lost device, its gone for ever. So if u buy in ebay but there is less chances of getting caught but better be safe and dont buy stolen GPS from ebay.