No smoking signs may be driving more people to light up, a psychological study suggests. 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. 'When I say "don't think of a pink elephant", I've just put the thought of a pink elephant in your head. 'A lot of public health messages are framed in a negative way...