Federal agency building managers are responsible for furnishing and installing suitable, uniform signs in the building, and in and around building entrance doorways and air intake ducts, reading "No Smoking," "No Smoking Except in Designated Areas," "No Smoking Within 25 Feet of Doorway," or "No Smoking Within 25 Feet of Air Duct," as applicable.
41 C.F.R. §102-74.335