No carry signs??

I'm in a state where a posted no gun sign holds the weight of the law... with that being said is there a specific sign that I need to look out for? Are these signs issued by local PD? Can private establishments put a sign up that suddenly becomes law? It feels like there is a fine line between responsible concealed carry and being a felon.-Purchase some land and build a private business (lets say car shop) and post a no gun sign clearly on the door, if a customer walks in carrying are they commiting a felony?? At what point does the area spontaneously become a no gun zone -Can somebody put a no gun sign on their own house? What if they teach piano lessons everyday in that house so it's also a place a business?I get it "just carry bro" but can someone please educate me via /r/CCW https://ift.tt/LWTg0xV