We're on the edge of rural, on a cul-de-sac, so we don't get a lot of door-to-door traffic, which I'm glad for. I don't post signs, though I've thought about it. I don't appreciate door knockers, whether they are for sales, charities, services, surveys, whatever. Our friends and family all know that we're not 'drop in' folks, so they don't do it. That means any knock at the door is either the UPS guy (he's okay) or someone wanting my money or my vote. If it's way early or way late, my response will be far more intimidating than it will during the day. Outside of the "polite" hours IronMonster noted above, then I assume it's either an emergency, or you're a threat.
If you read what Massad Ayoob has to say about answering your door, it might change how you do things. His video is kind of an eye opener - here is a copy of the video, though it's not posted by Mass himself:
If you read what Massad Ayoob has to say about answering your door, it might change how you do things. His video is kind of an eye opener - here is a copy of the video, though it's not posted by Mass himself: