The wall in the police station was covered in sheets of paper, one for every building in the sprawling Beijing apartment complex. Each sheet was further broken down by unit, with names, phone numbers and other information on the residents.
Perhaps the most important detail, though, was how each unit was color-coded. Green meant trustworthy. Yellow, needing attention. Orange required "strict control.”
A police officer inspected the wall. Then, he leaned forward to mark a third-floor apartment in yellow.