But this is where it gets really weird... my friend called the police and they told him to check the outside of their house, and that there might be a symbol chalked on the wall. Sure enough there was a discrete rectangle daubed by the front door. Apparently it's one of a set of signs made for others in the gang, though the police don't know what each one means – anything from 'don't target this house again' to ' there's a nice big telly in here to come back later for'.