The City of Savannah reviews, approves, and regulates all of its murals via the Historic Site and Monument Commission (HSMC) which operates under the Metropolitan Planning Commission (MPC). Below, you’ll find a link to the application - which includes the City’s definition of a mural. Due to the prevalence of preserved historical architecture within the city and the commonplace practice of needing a permit for any additions / changes - murals are pretty enforced. 

Also attached below, is the one-sheet provided by the HSMC / MPC - which also outlines the districts of enforcement within the city. 

https://www.thempc.org/docs/apps/hsmc/2018/instructions.pdf - "A mural, which is considered Public Art, is further defined as a singular, flat work of art applied on a building, structure, fence, or other object within public view. The work does not contain text, graphics, or symbols which advertise or promote a business, product, or service; nor does it promote a political candidate or party. The City Zoning Administrator will determine if a mural constitutes a sign and must, therefore, meet the requirements of the Zoning Ordinance. In the Savannah Local Historic District, a mural is considered a material change to a building and must receive a Certificate of Appropriateness from the Historic District Board of Review (HDBR) in addition to approval from the HSMC. It is recommended that a mural be reviewed by HDBR in advance of the HSMC.”