Locking your bike is pretty safe, but under the circumstance that someone gets it out of the lock, you would hope a bystander might take action.
The Meerkat Removeable Mudguard Lock is a safe way to lock a bike; however, if somebody figures it out then a witness would be helpful.
The Meerkat Removeable Mudguard Lock acts as a back tire mudguard, but can be removed, flipped up and connected to the lock. On the mudguard is the owner's height, sex, and age.
The trick is that hopefully an observant bystander would quickly differentiate between the description of the owner and a potential thief. Under theft conditions and police notification, information can be used from the bike to pinpoint its location on Google Maps.