Having done a bit of a Google have come to the following conclusions about the hoardings in Howard's original photos in #1.
The Depser AZ and DEPS hoardings seem to have been done by a graffiti artist who goes around painting this stuff and it means something to him. The AZ is for Astro Zombies who may be some sort of group of graffiti painters. The #atch and #amuk signatures are hashtags which may or may not identify the people painting this stuff or helping to.
This all presumably means something to the closed group of people doing it. In my opinion it is perfectly serviceable signwriting and no different than having an advert for Pepsi or whatever. Some graffiti shows great talent and it would be nice to see some of that on the hoardings but this is just sterile signwriting so nothing to get excited about. It is a perfect accompaniment to the derelict buildings behind and sets them off nicely, adding a signature to Dover's decay.
http://www.flickr.com/photos/theslog/8698845358/
http://www.flickriver.com/photos/theslog/sets/72157627852117149/