Beginning Wednesday, you’ll be able to put Johnny Cash on all your mail. A “forever” stamp honoring the country music legend will go on sale, coinciding with the end of a yearlong celebration of the Man in Black’s life and career. A free public concert in Nashville by family and friends of the singer also will honor his six-decade career. The 46-cent stamp will feature a 1963 image of Cash shot by Frank Bez during the photo session for the album “Ring of Fire: The Best of Johnny Cash.” Cash’s son, John Carter Cash, said the stamp is unusual, and...