A medical dressing for chest wounds, including a one-way valve that can be covered so as to protect against intrusion of airborne contaminants and to prevent passage of fluids in either direction, and including indicia visible using night vision devices but not visible in visible light to the naked eye in some embodiments. The indicia visible using night vision devices may be included in other medical apparatus, as well, so that the medical dressings or other apparatus can be used effectively during darkness, in combat situations, without being seen by enemy combatants not equipped with night vision devices.