Brad Meltzer has a show on the History Channel where he investigates various mysteries/conspiracies (2012, Masons, Confederate gold, etc.). One of the shows featured these stones. Title was ‘Apocalypse in Georgia’. Looks like you can get it from iTunes, but I wouldn’t be surprised if it’s not on youtube.
I saw that show when it aired. It was the first I heard of them. It was amusing.