A method of marking a unique code onto an edge of a sheet of material takes N stacks of sheet material, each stack having N1 sheets; prints a barcode uniquely identifying each stack on at least one edge of the stack so that each sheet of sheet material in the stack has the barcode printed on its edge. N1 stacks of sheet material are formed by collating the N stacks of sheet, wherein each of the N1 stacks has N sheets of sheet material, one sheet from each of the N stacks of sheet material. A second barcode uniquely identifying each of the N1 stacks is printed on at least one edge of the stack so that each sheet of sheet material in the stack has the barcode printed on its edge.