NEW YORK (Reuters)An Andy Warhol silkscreen of actor Marlon Brando, clad in leather astride a motorcycle from the movie “The Wild One,” is expected to sell for $20 million when it hits the auction block in November, Christie’s said on Wednesday. “Marlon,” a 1966 silkscreen that is one of the late pop artist’s most famous Hollywood portraits, will be part of the auction house’s sale of post-war and contemporary art.