The half-circle shape of the prison cell is based on old Roman catacombs. Coupled with the golden decoration around it, the cell turns into the Dark Sun logo.
The bas-relief higher on the wall is of a skull of the Dragon of Tyr (which would be the ultimate symbol of death in Dark Sun). It is based on Brom's cover for Dragon Kings.
The cell lock is a real thing, the first known lock, developed in Ancient Egypt of Iraq about 2000 BC.