My g/f rolls her eyes when we see smokers in a cafe- she knows I'm going to say something. I usually just point out to the smokers that it is illegal to smoke in cafes and that I don't want to breather their smoke- most of them are generally smoking with the sign right above them. I'm polite, but if the smoker continues- and they never have, I'm sure I could get creative.

Maybe I'll sit down at their table and talk on my cell phone loudly...
Maybe begin coughing really loudly until everyone stares at me (and them)...

Smokers...figure it out.