From 1963-1966 The Beatles did not want their fans to join them on stage while they were performing. Security, as well as Mal Evans and Alf Bicknell, were placed around the stage to prevent fans from getting to them. And if by chance a fan did make it onto the stage, that fan was immediately removed.
However, 50 years ago today, September 4, 1968 The Beatles actually invited fans to join them onstage in singing the "na na na na" refrain in "Hey Jude."
As the story goes, members of the British Beatles fan club in London were invited to take a bus to participate in a Beatles video session. Members of different cultures and professions were also invited. They were all taught the song (which couldn't have taken too long) and they did many, many takes of the song. The Beatle fans each tried to get the closest to his/her favorite Fab during the song.
I think the "Hey Jude" promo is in my top 5 favorite Beatles promos. It has something special about it. Seeing Paul with his big eyes and red velvet jacket sitting at the piano, singing the beginning of the song. Ringo concentrating on his drums wearing one of the ugliest green suits I have ever seen (and yet Ringo somehow pulled it off). John chomping away on his gum and for some reason wearing an orange bow tie around his neck, singing harmonies along with Paul. And George in brown, singing those background "ahhhhhs" without a care in the world.
And the fans -- oh those lucky fans. To see them run up to the stage and get pulled up closer to the Beatles. You have seen this clip so many times, that some of the fans seem like old friends. The boy next to Ringo playing the tambourine that shares a moment with the drummer, the girl with the blonde curls near Paul, the girl with the short hair that sits down next to George and singing along, and even Bill the Busker -- they all make the promo something worth watching over and over again.
I encourage you to go onto youtube and enjoy watching Hey Jude again for the 50th anniversary.