A self-described “American painter of signs,” Robert Indiana’s works explore visual culture, national identity, and personal history through symbols and colors inspired by signage and graphic design. The unmistakable black and yellow X-shape in USA 666 recalls railway crossing danger signs, which Indiana recalls seeing throughout his youth. The number six, as Indiana explained related to both the digits of his father’s birth month June, and the Philips 66 sign of the gasoline company that employed his father. The number also conjures up Route 66, an important American highway loaded with symbolism from novels and popular songs.