A substrate is printed with front side and back side markings in a first color ink. The front side when viewed with reflected light includes a first marking printed in a first saturation and a first symbol printed in the first saturation. The back side when viewed with reflected light includes: a second marking printed in a second saturation; a second symbol printed in the second saturation; a third marking printed in the first saturation; and a third symbol printed in the first saturation. The first marking, the second marking, and the third marking are printed to provide an interlocking pattern of low saturation color and high saturation color when viewed with transmitted light. The second symbol is visible, and the first symbol and the second symbol are not distinguishably visible, when viewed with transmitted light.