Do you think business that post no carry signs see a difference on their bottom line before/after said sign?
It doesn't take much of an impact to matter.
Here in Colorado, a couple of chains (I believe may Home Depot was one) put up no guns signs. The CSSA put this out, put pressure on them, and most of those signs came down. If a company takes it's sign down, I won't hold it against them -- in fact, I'll reward them for the return to common sense.
I think the real bottom line is ... if you don't put up a "no weapons" sign then it doesn't affect business at all.
Store owners don't like to see any money walking away. We need to keep up the message that "no guns = less money", whereas leaving the place unsigned and therefore neutral = no change.
Well DN ... I think you're over analyzing this.
So if putting up a sign sends even a single customer elsewhere, there is a loss. A successful business owner or even manager will notice that and want to stop it.