In states like Texas and Georgia, if businesses want to prohibit firearms on their premises, they can do so by posting conspicuous signs. State laws differ in the rights of business owners to refuse guns on-premises, however, the majority of states allow private businesses to choose whether or not to allow guns. You have to check with your state laws whether or not you can post a no guns sign. Like, in Wisconsin businesses are required to post a sign prohibiting guns that is at least "5 inches by 7 inches" and state the restriction on carrying a firearm.