I have literally been walking towards a place, money in my pocket intending to purchase something, seen the sign on the door and done a 180. Haven't been back. A Coleman Camping Store if you can believe that! You'd think a place that caters to outdoors types would be more hunter/firearms friendly.
With a house... Well, a no firearms sign tells me the current owners are either fascists or severely ignorant of the ways of the world. Tells me there's a good chance they aren't responsible homeowners either, so the place probably hasn't been maintained. Also tells me if they're capable of deluding themselves and lying to themselves to that level they'd probably lie to me too. I'd have no qualms about taking a pass on even considering their house.
There were a few no gun signs on businesses when we got cc years back. I haven’t seen a sign on a private business in years. The only “business” that can afford a no gun policy is the government.