Discovered this (among many others) at a kick-off event with the SDG 'On Tour' contingent, in London. We met outside the British Library, and saw some very cool TB tags - in particular one of the group had made wooden tags and scorched out the TB code - most inventive! Also very nice to meet anew cachers on this trip!
Thanks to TB owners for sharing, and please accept my apologies for such late logging (I've only just uncovered my stash of photos!)