Signal square

[1] It contains ground symbols to indicate visually the conditions on the aerodrome to over-flying aircraft.

[3] In the UK, the square internal sides should measure 12 metres, "bordered by a white strip 30 centimetres wide"[4] and "so located on the aerodrome that it is visible from all directions of approach".

[5] The Schedule 1, Section 9 of the Rules of the Air Regulations 2007 further illustrates the dimensions of each particular signal, e.g. both arms of the landing T should be 4 metres long and 40cm thick, and the dummbell sign should consist of three sections, each 1.5m long.

All dimensions shall be "subject to a tolerance of 10 per cent, plus or minus".

[4] The same documents include the H sign indicating a landing area for helicopters, commonly used on a helipad (but not a circle around the letter H), to be displayed in the Signals Area.