A UK traffic sign, diagram 106 of the The Private Crossings (Signs and Barriers) Regulations 1996. It would be mounted on crossing gates, to enable motorists to see the gate when closed across a roadway.
Regulations called for the sign to be 600 millimetres (24 in)
Drawn according to The Private Crossings (Signs and Barriers) Regulations 1996 and RSSB standards.
UK Government
This file: The Navigators