An Equity Card is proof of membership in an organization of stage actors such as the Actors' Equity Association

Actors' Equity Association

The Actors' Equity Association , commonly referred to as Actors' Equity or simply Equity, is an American labor union representing the world of live theatrical performance, as opposed to film and television performance. However, performers appearing on live stage productions without a book or...

 of the United States or the British Equity. For some exclusive clubs catering to show-business types, the card can be used to prove that they are indeed the actor and not an imposter.

According to the BBC

BBC

The British Broadcasting Corporation is a British public service broadcaster. Its headquarters is at Broadcasting House in the City of Westminster, London. It is the largest broadcaster in the world, with about 23,000 staff...

 website, the children who sang on Pink Floyd

Pink Floyd

Pink Floyd were an English rock band that achieved worldwide success with their progressive and psychedelic rock music. Their work is marked by the use of philosophical lyrics, sonic experimentation, innovative album art, and elaborate live shows. Pink Floyd are one of the most commercially...

's number one hit
"Another Brick in the Wall

Another Brick in the Wall

"Another Brick in the Wall" is the title of three songs set to variations of the same basic theme, on Pink Floyd's 1979 rock opera, The Wall, subtitled Part 1 , Part 2 , and Part 3...

(Part 2)" couldn't appear in the video because they didn't hold Equity cards .