If you are the owner of a building or property in Alabama that allows public access, and do not wish firearms to be allowed on the premises, you must comply to Alabama's gun sign laws pursuant to Act 2013-283 Section 6.
Code of Ala. § 13A-11-75 (c) The person or entity with authority over the premises set forth in subsections (a)(1)-(6) and subsection (b) shall place a notice at the public entrances of such premises or buildings alerting those entering that firearms are prohibited.