This sign provides cyclists with a way to warn of their presence on a bridge. 
 Used with <a href="//commons.wikimedia.org/wiki/File:Canada_Cyclists_Must_Push_Button_To_Warn_Of_Presence_On_Bridge_Sign.svg" title="File:Canada Cyclists Must Push Button To Warn Of Presence On Bridge Sign.svg">File:Canada Cyclists Must Push Button To Warn Of Presence On Bridge Sign.svg</a>.
Transportation Association of Canada
Manual of Uniform Traffic Control Devices for Canada