Lyric discussion by betch252 

Cover art for C Moon lyrics by Paul McCartney

L7 is from America. It was first used in Sam The Shams "Wooly Bully". Here is an explanation:

"The warning, "Let's not be L-7's"", means "Let's not be squares", from the shape formed by the fingers making an L on one hand and a 7 on the other"

When I lived in Liverpool, I thought it was to do with the postcode area "L7" being not so cool.