The cat clerics wear a cigarette in the ear, this is a reference to the first ever episode where Lister does this when feeding his cat Frankenstein
Diamond light Rimmer has a kiss curl in his hair just like Christopher Reeve when portraying Superman in certain movies about the character. EDITED TO ADD: This curl on the forehead is a known characteristic of most comic book and graphic novel portrayals.
Rodon keeps changing the way he wears his costume cat claws.