Before Florida did its state road reorganization in 1945, it had a different network with different route markers.
Unfortunately, the route markers had the route number in smaller type than the abbreviation "FLA." inside a blue diamond. Of course, that meant the number was not very legible to a motorist passing at 50 miles an hour.
But it's a nice marker and if you shrink the abbreviation and enlarge the number, you can have a uniquely recognisable icon for the state of Florida. Here below are examples for the state and county roads.