This is a variation of the technique a company called "Address America" teaches its distributors. Address America manufactures and sells reflective address signs. According to them it's a very effective techique. It involves taping a letter and a response form to, or around a home's door. If a homeowner wants a sign, they complete the form and tape it to their window (facing out, of course). The distributor drives by a day later looking for the paper in the window, get's the details, installs the signs, then either collects payment immediately afterwards, or leaves an invoice.