# Geneva Conventions Act 1957, Paragraph 4


At night or when visibility is reduced, the sign may be lighted or illuminated. It may also be made of materials rendering it recognisable by technical means of detection.
Fig. 5: International special sign for works and installations containing dangerous forces

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Source: https://www.legislation.gov.uk/ukpga/Eliz2/5-6/52/schedule/FIFTH/part/VI/chapter/34/paragraph/4 (the official version)
Page: https://openlegislation.uk/geneva-conventions-act-1957/schedule-FIFTH/part-VI/chapter-34/paragraph-4
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.