Holy misleading headline, Batman.
It's not United's entire fleet, as the headline implies. It's just their (relatively small) collection of Airbus A321neo planes.
The signs are not faulty. They're deliberately hardwired on, as they are in United's Boeing planes.
"The airline’s Boeing 737, 757, 767, and 777 aircraft already have no smoking signs “hardwired to stay illuminated at all times” according to the filing. United just forgot to ask for the same regulatory waiver for the A321neo as for these aircraft. This is a new plane type for the airline. They have 5 currently in service."