Signs are that smokers reject calls to stub it out.
Scientists say the messages have an "ironic effect" on smokers that increases their craving for tobacco.
Without being aware of it, they react to the signs by thinking of and wanting cigarettes.
"You get ironic effects when you couple information that people perceive with negation," said researcher Brian Earp, from Oxford University.
To test the theory, Mr Earp's team first primed a group of smoking volunteers from a town in New England, US, by showing them a number of photographs. Some included a no smoking sign in the background or at the edge of the picture, while others had the signs edited out.In a series of experiments, the researchers showed that participants who had earlier been shown no smoking signs were more drawn to smoking-related images such as ash trays and cigarettes.