The term, graffiti, originally referred to the inscriptions, found on the walls of ancient Greek and Roman ruins, e.g. in the Catacombs of Rome. The earliest example of what may be considered promotional advertising is considered to be found in Ephesus in Turkey where a drawing shows a heart-shaped hand, a footprint and a number. And yes, you've guessed it, this is probably an advert for a brothel!
Via hip-hop, graffiti has entered mainstream popular culture and is an example of the counter-culture becoming accepted by the establishment. Original works by Banksy, surely designed to be an irreverent, satirical dig at modern society have been preserved, removed and sold at auction for many hundreds of thousands of pounds. Now in private collections, has the work rather lost its point? Originally remaining anonymous and carrying out his work illegally - defacing public buildings, Banksy has now become a highly successful modern artist and his work can be found on cards, tea towels and posters, classic examples of brand extension. Self-promotion by stealth.