“Put a sign up that says "No Jehovah's Witnesses, or any other religion that shelters child rapists!"
In the UK you could be setting yourself up for arrest for inciting religious hatred with a sign like that. A sign stating no religious callers would suffice. All that I know respect that. If you are just on the do not call list then it’s most likely that someone will call by mistake every once in a while. Also, after a couple of years one of the elders out that day will call, in case you moved house. That’s how it goes here anyhow.