The mark consists of L-shaped green line having a substatially horizontal longer part and a shorter substantially vertical part extending from the left axial extremity of the longer part; a green outline of the L-shaped green line has a substantially horizontal part and first and second vertical parts extending from the axial extrmities of the horizontal part. Superimposed on top of the bottom part of the green outline is a blue outline having upper and lower spaced apart substantially arcs joined at the respective ends by blue vertical ends. Within the blue outline "VISORVU" in black letters appears.