4.—(1) A plate or structure warning marking may only be placed in conjunction with an upright sign with which it is associated.
(2) An upright sign which has an associated plate or structure warning marking may be placed with or without that associated plate or structure warning marking.
(3) Paragraph (2) does not apply in relation to a particular sign to the extent provision is made elsewhere in these General Directions about the placing of the sign with an associated plate or structure warning marking which contradicts paragraph (2).