A billboard was a structure that displayed advertisements. They were commonly placed outside commercial buildings and alongside roads.
In 1986, the services of British Airways were advertised on a billboard in downtown San Francisco. (Star Trek IV: The Voyage Home)
On December 27, 2000, Shannon O'Donnel was driving through Indiana at 5:00 am when she saw a billboard mentioning Portage Creek as the future site of the Millennium Gate. (VOY: "11:59")
Several billboards were displayed outside the Toronto Eaton Centre in 2022. (SNW: "Tomorrow and Tomorrow and Tomorrow")
In 2024, there was a billboard somewhere in the Los Angeles area that involved getting assistance from a lawyer regarding a traffic accident that led to an injury in one's car. (PIC: "Assimilation")
In 2399, a billboard bearing the name of Kasidy Yates-Sisko's shipping company, Kasidy Yates Interstellar Freights, was present on Earth in Greater Boston. (PIC: "Remembrance")