301.06 (1) Except where the direction of the wind at an aerodrome can be determined by radio or other means such as smoke movement in the air or wind lines on water, the operator of the aerodrome shall install and maintain at the aerodrome a wind direction indicator that is
(a) of a conspicuous colour or colours;
(b) in the shape of a truncated cone;
(c) visible from an aircraft flying at an altitude of 300 m (1,000 feet) above the wind direction indicator; and
(d) illuminated when the aerodrome is used at night.
(2) When an aerodrome is closed permanently, the operator of the aerodrome shall immediately remove all of the wind direction indicators installed at the aerodrome.
From Canada’s AIM
(iii) If it is necessary for an aircraft to cross the airport before joining the circuit, it is recommended that the crossover be accomplished at least 500 ft above the circuit altitude.
From Aerodrome Standards and Recommended Practices, TP 312
The colour or colours should be so selected as to make the wind direction indicator clearly visible and understandable from a height of at least 300 m, having regard to background. Where practicable, a single colour, preferably white or orange, should be used.