I've had a sign up for 6 years now, and your right just a slight reduction in violators. Alarm companies are the most common offenders, I think they believe that my alarm company sign in the yard is an invitation for competition to ring the bell. I actually kind of enjoy answering the door to find a sales person at the door. I usually wait for them to go through the pitch and respond I don't want to change to a company with employees that can't read. Yesterday two girls came to the door and one is training the other, I suggested that teaching some basic reading skills would be a good place to start. Others I have used are "You speak very much like an American, amazing for somebody that can't read". I just don't answer the door most of the time, eventually they leave.