The MED Mark of Conformity confirms that a product or piece of equipment is approved for use on board EU member state ships and ships of countries which have agreed to apply the Marine Equipment Directive 96/98/EC. This is sometimes referred to as the ‘wheelmark’ or ‘wheel mark’ and also known as M.E.D/MED approval or certification. It provides confirmation that the equipment or product is suitable for marine industry use.

http://blog.pfannenbergusa.com/pfannenbergs-patrol-alarms-are-the-only-med-approved-devices-worldwide