Yes, a "No solicitators" sign on your door or if you have a window next to your door, say a side window.
I live in a private subdivision, it even has a large street sign at the front of the subdivision that says "No solicitators". Your best bet (esp if that happens often) (and you have that warning sticker in plain and easy to see view somewhere on your property).
Yet even so people of all sorts are spamming my door to sell me on something.
Then you can do what we do here:
1. Ask them to wait at the door, make an polite excuse such as you have something on the stove and need to put it on the back burner. Once you leave, quickly call the police (not 911 / emergency) and give a full description.
Here at my house, usually within 5 minutes (yes, 5 minutes OR less) at least 3 squad cars start cruising our subdivision, and quickly, as if a murderer is loose. It is quite funny to see a group of Mormons surrounded by the police with that street's neighbors all watching as they get arrested for trespassing.
2. Always remind yourself of "The Nine Satanic Statements" and "The Eleven Satanic Rules of the Earth". They are of course what the Satanic Bible teaches and are great in providing yourself, self control, and patience to be 1 up on them.
3. Now, if you are a "Funny guy" (or quite possibly what most people would refer to as an asshole) or just me (a Trickster - ala "TriKster") (my nick). Have an air horn, the kind you get for parties, they are small, cost almost nothing and are loads of fun to have. I will cover at least 2 of the things these air horns are fun for below. (silly string and authentic looking water gun
pistols are fun also). Plus I am retired, young and usually at
home 90% of the time.
A. Walk outside your door, (never invite any of these people
into your house, not all things appear as they are. You
could be looking at a potential theif or someone with evil
intentions). As they begin to talk use your can of air (ala
the air horn) and with each try they will be unsuccessful
as it is hard to get a word in edge wise when someone is
blowing an air horn at you everytime your lips begin to
move. This also provides a way to alert the nieghbors!
B. The air horn also works great for tele-spammers also.
Finally, the reason why I say never invite these people into your house, no matter how nice or no matter what they have to sell, is if you are not prepared to be somehow hurt or ripped off things could go down very fast. Also these "spammers" prey on moving about during the day, to see what houses have people at home. Kind of like profiling and watching a bank prior to a robbery.
Believe it or not as paranoid as it may seem these things do happen. Be prepared to protect yourself once again at all costs.