The international distinctive sign of civil defence is an equilateral blue triangle on an orange ground when used for the protection of civil defence organizations, their personnel, buildings and matériel and for civilian shelters. (item 4, Article 66 of Protocol Additional to the Geneva Conventions of 12 August 1949).
It is recommended that:
The international distinctive sign shall be as large as appropriate under the circumstances. The distinctive sign shall, whenever possible, be displayed on flat surfaces or on flags visible from as many directions and from as far away as possible. Subject to the instructions of the competent authority, civil defence personnel shall, as far as possible, wear headgear and clothing bearing the international distinctive sign. At night or when visibility is reduced, the sign may be lighted or illuminated; it may also be made of materials rendering it recognizable by technical means of detection.