Non Smoking

Is it appropriate to put "non smoking occasion" on the invitations?

While you could print it if you want, those who smoke will find a place/way to do it anyway. It is an addiction and they need a fix. It's unrealistic to expect some smokers to go all day/night without a cigarette, much as you would like it. Printing it on the invitation may offend some guests and stop some smoking guests from attending, which you probably wouldn't want to do.

It somewhat depends also on where the wedding/reception is. Most people will not smoke in a church (and if there are signs posted no smoking, they will simply go outside). Many hotels/restaurants are no-smoking in public areas and many have separate smoking rooms or areas designated for smokers. You can post no smoking signs at your reception site if there are none already. Or, smokers will again simply go outside to smoke. If you have this at your parents house or some other relatives' house, you can certainly tell guests and post signs that say NO smoking in the house.