June 22, 1955, Walt Disney received a memorandum from WED (the predecessor of Disney Imagineering) about the wording of the plaques that he wanted above the Disneyland tunnel entrances. Walt had asked for the plaques to set the stage for his guests before they passed under the train station through the tunnels, which have been referred to as the park’s “stage curtain.”
The June 22, 1955 memo included a draft reading: “Disneyland - Where you leave today … and visit the world of fantasy, yesterday, and tomorrow.” Walt made some slight edits and today the signs read: “Here you leave today and enter the world of yesterday, tomorrow and fantasy.”
The plaques weren’t quite ready for Disneyland’s opening day on July 17, 1955. According to the Disney Archives, the exact date they appeared is unknown though it was sometime later in 1955.
This particular version of the plaque was designed by Paul Hartley in 1969. Prior to that they were hand-painted by the sign shop.
Growing up in Los Angeles in the 70s/80s we visited Disneyland on a regular basis and often after school, before "Annual Passes".