Here's a tactic you might want to try. Tell them they are welcome to come in and share their system of belief with you, as long as they're willing to give you equal time to explain why you are an atheist (or agnostic). I wonder how many takers you'd get? Then again, if you value your privacy and feel their very presence on your porch is an intrusion, just keep pointing to your sign--they are, after all, soliciting your valuable time!

It's free? Really? So, I guess they don't tithe? Free, my @$$.

Good for you. I suppose they didn’t think the sign applied to them, with their special status as self appointed god disciples!