Why haven’t they put out airplane ‘no smoking’ signs?

Surely I can’t be the first person to have noticed that while cigarettes are unlit, the ‘no smoking’ signs remain lit. There have got to be people at Boeing and Airbus who are concious about these redundant signs.

My last recollection of smoking being permitted onbaord an aircraft was 1997. I’ve been on 20+ airlines since then and I’ve noticed that every single one of them has had this sign, while none of them actually permitted smoking onboard. Some of them are probably still using older planes and ergo still have the signs. That being said, some of these airlines weren’t even existance when smoking was banned from commerical flights. So, why do they have these signs?

Are airlines just trying to be prepared incase smoking is permitted once again? Or was nobody able to think of a more useful sign to replace it with? Personally I would be in favour of a ‘no kicking the seat in front of you’ sign.