To put an end to this incessant parade of annoyance, I went looking for a simple "No Soliciting" sign on the Internet to tape to my door. I couldn't find anything simple and suitable, so I made a plain one myself, printed it, and stuck it on my door. Will see if it helps.
Feel free to click and download the image and use it as you please. Shrink it, cut it, edit it, whatever you want. Color print works best, but I think it'll come out fine with b&w too. Just don't go selling it door-to-door 🙂