Article 6
The exemption given in respect of regulation 5 shall apply in relation to any exempted vehicle only while instructions for the operation of any door which is operated by a control device to which the exemption relates are displayed on a sign:
(a)
which is placed on or near that door and on the same side of that door as any such control device; and
(b)
on which the letters, numbers or diagrams contrast with their background and are identifiable by touch.