# The Traffic Signs Regulations and General Directions 1994, Paragraph 4


The following legends may also be displayed on a variable message sign
(a) “SIGNAL UNDER TEST”
(b) “SIGN UNDER TEST”
In either case the message may be used with a pattern displayed which has no particular meaning but which is designed to test the functioning of the sign or signal.

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Source: https://www.legislation.gov.uk/uksi/1994/1519/schedule/15/paragraph/4 (the official version)
Page: https://openlegislation.uk/traffic-signs-regulations-and-general-directions-1994/schedule-15/paragraph-4
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.