Your translation from Italian is just as funny as the original translation from English into Italian. "E' pericoloso sporgersi" is a warning about the danger of "sticking your head too far" out of.. or into...

Italian warning signs are just that: warning. The "Grazie per non fumare" is not a warning. It should read: "Vietato fumare". This sign carries an order and would leave the person the choice and responsibility for the actions taken and possibly suffer the consequences for it. This approach leaves the person with the dignity of making choices rather than the guity feeling for not having satisfied the request for which has received anticipated Thanks. Hence the difference between English and Italian.