NFPA 99-2012: 18.104.22.168.8, 22.214.171.124.9
Central supply locations containing positive pressure gas cylinders other than oxygen or medical air shall have a label on the door that says:
Positive Pressure Gases
NO Smoking or Open Flame
Room May Have Insufficient Oxygen
Open Door and Allow Room to Ventilate Before Entering.
Locations containing central supply systems or cylinders containing only oxygen or medical air shall have a door label that says:
NO Smoking or Open Flames