No need for such unnecessary sign. Although best to NOT use cell phone near gas dispenser. Just leave it in your pocket while holding the gas dispenser, or go sit in your car if you must make a phone call. The gas will shut off automatically when tank is full.
In 55 years of filling gas in my cars, ONE time I left left the gas nozzle in the car’s gas hole, and drove off in a hurry. The gas dispenser nozzle was stuck in my car. But they had a quick release joint at the end of hose, so not much harm done except spill a bit of gas on floor of gas station. The attendant just smiled, she had seen this many times before, obviously.
I saw a girl sit her car and talk on her phone while the gas was pumping into her car. The pumps are made to cut off once the tank is full. From what I understand, due to a malfunction, this time it didn’t and and approx 5 gallons of gas spewed onto the pavement before another car’s driver walked over and shut it off. She insisted to the clerk she shouldn’t have to pay for the extra gas. I was present for the tail end of the discussion and the clerk was not amused. So for that idiot, yes, talking on the phone while pumping gas was not exactly a good idea.