"Spitting gum is anti-social. We want this campaign to start changing people's behaviour and encourage them to think about better ways of disposing chewing gum." said Roni White, Ealing Council's anti-graffiti manager.
The posters, called GumTargets, will be displayed along Acton high street for a year and if successful they might appear in other places too.
The campaign follows trials in Luton and Bournemouth which showed a reduction in the amount of gum left stuck to the streets.