Over the course of a career that stretches back 20 years, singer-songwriter Citizen Cope (aka Clarence Greenwood) has not become a household name, even though he probably should be. His ballad “Sideways” was featured in TV soundtracks for Grey’s Anatomy and Scrubs, and his compositions have been recorded by Carlos Santana, Dido and Richie Havens. Cope brings his solo acoustic tour to the Music Box Supper Club, where he performs at 8 p.m.