Most posted signs I see aren't legal anyways, there is a reason they have specifications
Tennessee No Guns Signs
As of July 1, 2016, amendments to Section 39-17-1359, which made changes to the requirements for posted signs, will take effect. Tenn. Code Ann. § 39-17-1359 (b) (3) (A) A sign shall be used as the method of posting. The sign shall include the phrase "NO FIREARMS ALLOWED", and the phrase shall measure at least one inch (1") high and eight inches (8") wide. The sign shall also include the phrase "As authorized by T.C.A. Section 39-17-1359". (B) The sign shall include a pictorial representation of the phrase "NO FIREARMS ALLOWED" that shall include a circle with a diagonal line through the circle and an image of a firearm inside the circle under the diagonal line. The entire pictorial representation shall be at least four inches (4") high and four inches (4") wide. The diagonal line shall be at a forty-five degree (45deg.) angle from the upper left to the lower right side of the circle.