noun, verbal noun, の adjective
If smoke is prohibited you probably shouldn't smoke. Aka no smoking, okay?
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
How could I forget that this is a no smoking area?
I've decided to make every Monday a no smoking day.
I told my mom to quit smoking and she told me that if she did, she would probably go crazy and my parents would get divorced.