We've all seen these signs that say "no soliciting" on doors. My favorites are the ones on places that have "SALE!" right beside them.
So they can harass you when you come in, ("So what's it gonna take to put you in this car/satellite dish/blender/carpeting today?") but you can't ask THEM to buy something from you. ("So what's it gonna take for you to shut up and listen for a second?")
Also, this isn't a legally binding sign...you can't be sued or arrested just because somebody goes out and buys a $5 sign. If it was a legal sign with the law behind it, the democrats would have a tax on it and you'd need a lawyer to notarize it and there would be fine print, etc, etc. The sign would cost about $300. And you'd have to buy it from someone (a government authorized one) and they might come to the door and you be right back where you started from.
With or without the sign, I suppose if they told you to leave and you didn't, you'd be in trouble for trespassing, but if as a salesman you stay when someone says no and tells you to leave, you are missing the point of selling anyway.
I've thought to combat this I could wear a shirt that said, "No Rejections." Or I could buy one of these "no soliciting" stickers and put it on the window of my car. It would save me from answering the "do you want fries with that?" question.
I've always wanted to sell these worthless signs door-to-door...if they said no, I'd just say, "Okay, see you tomorrow!"
