E Pericoloso Sporgersi is actually the first Italian phrase I ever learned, when I was eight years old. My parents, brothers and I spent a few months near Geneva, Switzerland, where my father was working, but we often traveled by train to see other parts of the country and visit nearby parts of France. E Pericoloso Sporgersi was affixed under every window on practically every train.
It is dangerous to lean out.
The sign was in other languages, too (French: Ne Pas Se Pencher Au Dehors; German: Nicht Hinauslehnen), and English. But decades later, I still only remembered the Italian, perhaps because as a young child I thought E Pericoloso Sporgersi sounded quite silly (try saying it fast a few times), not to mention that the French is a bit of a tongue twister and the German has the harsh sounding nicht. Or maybe I remembered it because the Italian was the first line of the warning sign, followed by the other translations (English was last). Was this because it was thought that Italians would be more likely than French or Germans to lean out the window, therefore it had to be most visible? Or maybe the signs were produced in Italy, so Italian came first out of national pride.
Regardless, on my first train ride in Italy, from Venice to Bologna, I looked for the sign and was dismayed not to find it. Ditto on the train from Bologna to Ravenna. Had everyone learned in the intervening 30+ years to not lean out of train windows? But from Ravenna to Florence, where I changed trains to continue to Rome, the little sign was displayed under the window of my local train, just as I remembered. I photographed it. There was still no Spanish translation on the sign - I will leave you to develop a theory as to why.
The local train slowly wound its way through hilly countryside covered with farms and vineyards and sprinkled with villas and castles. I was tempted to stand up and lean out the window to take some photographs, but I did not.