Why do airplanes have ashtrays? Because people don't listen and lots of fires started in the bathrooms after it was officially banned in 2000. Yes, not that long ago.

Oh, and

"There is a switch at the bottom of the overhead panel, next to the seat belt sign, slightly right of the middle. Flip it and they will extinguish. The functionality is a bit more complicated than it would appear, since it feeds into the central aircraft electronics.

Out of interest, this button no longer exists on the Boeing B787, suggesting that it is on the way out. Only the seat belt option remains.

The slots for no smoking are being increasingly 'redeveloped' into a sign for electronic devices instead on some types. They just put a no smoking sticker on the seat in front of you to fulfil the same function. I do not know if they cockpit text has been modified on the aircraft that undergo this modification."