Tiles. But not on a harsh rectangle. Used Painters Offset Pattern to help build this. Top half of picture is repeated in bottom half but 180 degrees out of phase (that's pi radians for you geeks). The two halves interface seamlessly. The whole unit tiles on a normal rectangle, but because of the doubling and offset you get a much nicer tile than the familiar pulsing in your face grid that you see so often. The letters are available here.