Polite way to inform door-to door religious groups that I am not up for conversion?

I've been getting knocks at my door at least once a week now from one or another religious organizations doing evangelical missions. I appreciate that this is part of their duty to their respective churches, but I am honestly not interested, and have tried to politely tell each of these organizations that I am not interested on many occasions. Would it be tacky to hang a "no soliciting" sign in my entryway, or something that says that we are not looking to convert to another religion? PLEASE>>> Do not start any discussions on the validity of religion or p value judgements on religious folk on this question, it's not relevant here.