We're a bit busy to do the theory - you'll have to look at the AdBusters site. Below, some posters in London, June 1998. One particularly irritating car ad was targeted at the time the UK government launched its Transport White Paper and RTS its Green, Black and Red Paper.

Two identical posters, slogan: 'enjoy'. Additions: 'N London Street Party Noon Euston June 6 OR..' [on next poster] 'MORE POLLUTION'
Painted as if the car is graffitied: 'Reclaim the Streets' [on front of car] 'June 6th 1998'
Poster slogan: 'Quality is a right not a privilege'; Addition: 'Clean air is a right'
Poster slogan: 'Amuse the kids. Park it sideways in the garage'. Addition:  'and leave it there. June 6th 98', etc
Poster image: car with Noir shadow. Addition: 'A shadow over us all'

Or hit your [back] button...