It seems to be fairly low-resolution and low-quality compression and I didn’t see any clear sign of editing that I (a non-expert) can see.
I did search up a ton of Atlanta police car images and didn’t find any with that slogan.
But when I searched for
atlanta police “one city under god”
although I found no images, I did find a Facebook comment from someone:
“Guy Driskell I like that Kendall County patrol cars. Here in my town of Atlanta Texas our cars have “One City Under God” on them.”