Every pair of PURE lenses will have a Fog mark ( PURE ) on the lens surface. As it is a hidden marking, which may be too difficult to find it without any instructions, this can be identified by fogging the lens OR you are advised to ask opticians to point it out for you. Due to different size of frame, this fog mark may be cut out during lens cutting process; in this case you may check the product authenticity card or lens’s packaging bag that will dispatch with your pair of glasses.