Hmmm I see that this is a controversial topic. Which is why they work so well.
I will answer the question about how to avoid the pissed off people. that's to set up a Google Voice number that is specific to ONLY your bandit signs. This line doesn't get answered. Instead, you have someone record a voice over greeting (so that it's not your voice) that gives the caller specific instructions on what to do next.
1. Leave their name, phone number, property address they want to sell and a good time when you can call them back.
This simple technique screens out a little bit of everyone that doesn't need to be calling int he first place. (Code Enforcement and Non Motivated Sellers).
Double check to make sure that the address is legit and only call back those that followed instructions.
I have an entire Bandit Sign Scandal story on my website that you guys might want to check out. I've been through the ringer with bandit signs and the city - but you know what? We cant make everyone happy, no matter what we do, so might as well do what makes us happy.
Take care