The mark consists of The numbers 180 divided horizontally along a horizontal axis running through the numbers at an intersection where the lines forming the number 8 cross one another. The horizontal axis further dividing a circle containing the numbers 180 into equal halves. One half of the circle being filled and containing the number 180 as open spaces and the other half of the circle being unfilled and containing the numbers 180 as line drawings. The circle further having a line border circumscribing the circumference of the circle and having spaces dividing the line border into two halves at the horizontal axis and dividing the line border according to corresponding halves of the circle. The net effect being that the numbers 180 can be visualized regardless of whether the filled or unfilled half of the circle is oriented above the horizontal axis.