In shots on the Arizona City streets the wall painted sign "Tienda De Matteo" is seen. This sign is left over from the Season 3 Episode 14, "A Lamb to the Slaughter" in which Caine pays a debt to the store owner Matteo in a Mexican coastal city.
At the beginning of the episode where Caine and Serenity are talking in the graveyard, there is a shuttle bus visible in the background in multiple shots.