We're pathetically obedient. We queue and walk where we're told to, and all because it's printed on a sign.
There is a massive body of research about the psychological effects of signs, perhaps because they're an easy way to rope members of the public into an experiment without asking permission: erect a sign, stand somewhere inconspicuous, and watch how people respond. In general, it seems, we're pathetically obedient, queueing where we're told to queue, walking where we're told to walk, just because it's printed on a sign. (Would-be fascist dictators, take note.) Studies suggest “invoking norms” is a very effective tactic: to get people to reuse hotel towels, tell them lots of other guests do so. And specificity matters: asking hikers to keep to the footpath to preserve particular trees is better than asking them to protect the forest, which, in turn, is better than “save the planet”.
Most intriguing, though, are those studies that demonstrate how often signs have the opposite effect from that intended. As Tom Vanderbilt wrote recently in Slate, traffic safety authorities now largely agree that “Slow: Children At Play” signs save few, if any, lives, lulling residents into imagining the risk is lower while subtly implying there's no need to watch out for children except close to the signs. And an Oxford University study published earlier this year found related “ironic effects” for No Smoking signs: seeing them, it concluded, prompts smokers to crave a smoke. Smokers shown photos with the sign in the background showed a more positive reaction to pictures of ashtrays and cigarettes. The signs may work in a narrow sense – preventing smoking where they're displayed – but only at the price of exacerbating the broader problem.