The singer Common sent a shout-out to Hong Kong pro-democracy protesters -- perturbing some mainland Chinese fans in the process -- during an acceptance speech at the Oscars on Sunday night. He and singer John Legend won the Academy Award for best original song for “Glory,” from the film “Selma,” about the Martin Luther King Jr. and the American civil-rights movement in the 1960s.

Common referenced a bridge in the town of Selma, Ala. where Mr. King had marched, saying it connected people across the world who were fighting for...