I've noticed that Alabama uses red shields for a few county routes. I've tried to figure out if there's a pattern to it - do they lead to firehouses, are they dead-ends, and so far I can't come to any definite conclusion. Anyone?
Where specifically did you see these? I don't ever recall coming upon any during my Deep South years. For that matter, the only location in Alabama where I saw a county route shield that was something other than the blue pentagon was in far southern Washington County where a couple routes were marked with white triangles instead.
In Cherokee County (and possibly others), black on white pentagons are used for driveways. The gold-on-red pentagon was on US 278 EB in Cullman County, but I saw a few others as well (don't know where). Co Rd 1168, a short dead-end a few miles west of I-65, if you're looking on Google Maps.
Cleburne County uses white on green for driveways and in Dekalb County the county shield is used and the words Dekalb County is taken out.