The mark consists of a circle having extending inwardly from the perimeter thereof four lines, each terminating in an angled configuration near the center of the circle, one line originating at the topmost point on the perimeter of the circle and extending downward, and the other lines originating at points on the perimeter of the circle 90, 180, and 270 degrees clockwise therefrom, respectively. Within the circle are three dashed-line concentric circles, and four small solid-filled circles. Exterior to the circle, and parallel to the perimeter thereof, is an inner curved line, extending counter-clockwise about four-fifths of the way around the circle and terminating in a triangular, pointed configuration. Exterior to the inner curved line, and also parallel to the perimeter of the circle, is an outer curved line, its point of origin being offset about 90 degrees counter-clockwise from the point of origin of the inner curved line, and extending clockwise about four-fifths of the way around the circle and terminating in a triangular, pointed configuration.