Mc Manus' "meditation" circle that he draws on the floor. Around the same time as the "Jericho" puppet is introduced...In the last season, when "the walls came tumbling down." Take a look at a map of Jericho◊.
HBO's Oz was a pretty disturbing show in its time with all the graphic depictions of drug addiction, alcoholism, self-mutilation, rape, sadism, torture, bullying, suicide, murder, etc. Consider this though: some death row inmates have claimed in interviews that the prison experience depicted in this show was BETTER than life in a real prison, saying that this show was cleaned up for television. HOLY SHIT.