This is the unofficial official nickname for the state of Alabama. It has been on the car tags there for years and years.
The official nickname of the state is the Yellowhammer State. Many folks think this comes from a species of woodpecker, but they are wrong. During the Civil War, the cavalry troops from Huntsville, Alabama showed up at Hopkinsville, Kentucky, where Gen. Forrest's troops were stationed. These folks from Alabama had brand new uniforms with bright yellow cloth on the sleeves, collars and coattails. They became known as the Yellowhammer Company, and that appellation eventually came to be applied to all the troops from Alabama.