Slave Stone?

[Headhunter23]

I saw this at an antique store and was wondering if anyone knew what it was.
All it said on it was Slave Stone.
Could it have been part of an old Slave Auction House? Or is it something simple I am missing completely?
Thank you

 

[fyrffytr1]

How big is it and what is it made of, pottery or stone? If it is like what I have, it is one of a set that was made to encircle a grave. Many were made by slaves and I have two that came from an early 1800s pottery near Ft. Gaines, Georgia. I don't know why the two black bars showed up in the picture.