Department of Transport, Traffic Signs Manual : Chapter 4… (2013)
“ The legend "for" and a distance may be added 14.1 The low-flying aircraft sign, diagram 558, is for use on roads skirting or in the vicinity of airfields where road users are likely to be startled by low-flying 600 aircraft or by sudden noise from aircraft. A plate to diagram 558.2 indicating "Gliders" should be added where appropriate. A plate to diagram 773 (see para 21.3) should be mounted below the sign if wig-wag signals are installed to control the movement of traffic during the take-off or landing of aircraft. ”
