During the opening sequence in which Batman rescues Jonah Hex and they capture the royal flush gang, two signs reading "Sergio" are seen at the railway station. This is likely a nod to Sergio Leone, director of 'spaghetti westerns' (A fistful of dollars, the good, the bad and the ugly), so named because they were Products of an Italian director, Italian production company and often filmed at least in part in Italy.
The Old West version of the Royal Flush Gang appears to be missing a member. Normally, the Royal Flush Gang consists of five members: King, Queen, Jack, Ten and Ace. "Ten" is missing in this particular iteration of the group.