@David-and-Annie0 Here's another smoker's perspective. Yes, I think a couple signs in the house is a good idea. But like @Branka-and-Silvia0 said, most smokers will be respectful and not smoke in the house. The ones who aren't, won't give a FF about the signs.
Of course, smokers shouldn't book properties which clearly state no smoking. But the fact is, from reading many posts on this subject here over time, is that some will. The thing about smokers is that we're good at denial- we can think, "Oh, no problem, I'll just go out on the street to have a smoke", but when it's one AM and cold out, or everyone else is sitting out on the deck having a glass of wine, we might think "Oh, I'll just have one here, the hosts will never know, it's outside , for pete's sake". (I actually don't do this- I've always gone out on the street to have a smoke if I'm staying with someone who forbids it, no matter whether it's cold or raining- that's the price I pay for a bad habit)
So you have a choice- you can adamantly state No Smoking anywhere on the property, then be faced with evicting guests who are ignoring that, or finding you have to do a mega-clean to get rid of the smell and the butts, or try to get them to pay for extra cleaning after they leave, or you can say you really don't want people to smoke but set up an area where it won't blow back into open doors and windows and have a safe place for butts- like a bucket with sand, for those who simply must smoke.
When my daughter went and got a nose ring when she was 15, just because I didn't yell at her or ground her, didn't mean I was condoning it. There's plenty of things guests might do that we don't condone, but it just seems practical to come up with ways to mitigate stuff that guests might do regardless of our rules.