The International Civil Aviation Organization (ICAO, pronounced /aɪˈkeɪ.oʊ/; French: Organisation de l'Aviation Civile Internationale, OACI), is a specialized agency of the United Nations. It codifies the principles and techniques of international air navigation and fosters the planning and development of international air transport to ensure safe and orderly growth. Its headquarters are located in the Quartier International of Montreal, Canada.
The ICAO Council adopts standards and recommended practices concerning air navigation, its infrastructure, flight inspection, prevention of unlawful interference, and facilitation of border-crossing procedures for international civil aviation. ICAO defines the protocols for air accident investigation followed by transport safety authorities in countries signatory to the Convention on International Civil Aviation (Chicago Convention).
If you have some questions, you can reference to http://www.icao.int/about-icao/Pages/default.aspx.
We excerpt some provisions from ICAO Annex 14, 6th Edition, July 2013 as following:
Annex 14 to the Convention on International Civil Aviation
6.2.5 Overhead wires, cables, etc., and supporting towers Marking
18.104.22.168 Recommendation.— The wires, cables, etc., to be marked should be equipped with markers; the supporting tower should be colored.
Marking by markers
22.214.171.124 Markers displayed on or adjacent to objects shall be located in conspicuous positions so as to retain the general definition of the object and shall be recognizable in clear weather from a distance of at least 1 000 m for an object to be viewed from the air and 300 m for an object to be viewed from the ground in all directions in which an aircraft is likely to approach the object. The shape of markers shall be distinctive to the extent necessary to ensure that they are not mistaken for markers employed to convey other information, and they shall be such that the hazard presented by the object they mark is not increased.
126.96.36.199 Recommendation.— A marker displayed on an overhead wire, cable, etc., should be spherical and have a diameter of not less than 60 cm.
188.8.131.52 Recommendation.— The spacing between two consecutive markers or between a marker and a supporting tower should be appropriate to the diameter of the marker, but in no case should the spacing exceed:
- 30 m where the marker diameter is 60 cm progressively increasing with the diameter of the marker to
- 35 m where the marker diameter is 80 cm and further progressively increasing to a maximum of
- 40 m where the marker diameter is of at least 130 cm.
Where multiple wires, cables, etc., are involved, a marker should be located not lower than the level of the highest wire at the point marked.
184.108.40.206 Recommendation.— A marker should be of one color. When installed, white and red, or white and orange markers should be displayed alternately. The color selected should contrast with the background against which it will be seen.
You can also look at the full version of the PDF of ICAO Annex 14, 6th Edition, July 2013.