Electronic signs such as this one usually flash messages about construction or crashes, but this specific sign located near the South Carolina-North Carolina state line started warning drivers to be on the lookout for zombies, hunters and tanks.
Among the messages flashed on them were these ones: Zombies Ahead, Watch for Hunters and Be alert for Tanks. Authorities believe (no wonder) that the signs had been tampered with.
They also say that, so far, there have been no reports of the undead or tanks. Which is great.
This is the source if you still don't really believe it.