Careful travellers mark all their property before flying from home. Door entry smartcards can also be tagged. Smartcards can be specially printed with magnetic strips. Smartcards access is controlled but still safe if a person loses the Smartcard. Travelling Salesmen use tagged property.
Fences dont buy marked or tagged stolen goods.
Lost Smartcards can be returned. Found Smartcards can be returned by Police. People and property owners love tagged or marked property. Paintings and antiques can have property identification marks covertly attached. Lost and found service on the Internet.