No Smoking
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.
ここは禁煙スペースです。
This is a non-smoking area.
このホテルは、全客室禁煙です。
All guest rooms at this hotel are non-smoking.
僕は禁煙パッチを使って禁煙しました。
I quit smoking using a smoking cessation patch.