L7
From Tardis Wiki, the free Doctor Who reference
L7 was at least American slang for square or, in one sense of the word, straight. Jessica Willamy, then an enthusiastic member of the counterculture movement in the Haight district of San Francisco, thought Ben Jackson "L7-square" upon meeting him in 1967 because of his hair and clothing. (PROSE: Wonderland)
Behind the scenes
The term derives from the fact that if you put an L and a 7 together, it forms a square.
