The through-line that makes “Sign o’ the Times” an American Dream anthem for the Hip-Hop Nation is its honest glance at the nation’s ills. Like Marvin Gaye’s “What’s Going On” of the Vietnam era, Prince’s “Sign o’ the Times” examines a litany of problems then plaguing the country. “In France, a skinny man died of a big disease with a little name,” Prince sings, mentioning AIDS — relatively new in the world at the time — in the very first line. “By chance his girlfriend came across a needle and soon she did the same,” he continues, with a heroin allusion. The first verse ends with references to crack, machine guns and Chicago’s Gangster Disciples gang.