I generally lurk to see what’s going on, and thought I should comment on this.
I don’t know of any issur per se, however, you should be aware that there are a number of images on the standard playing cards that are directly linked to Avoda Zara. One example is the “club” that is an old symbol of Avoda Zara symbolizing the “trinity” (3 are really 1 kind of idea). The trinity idea predates cristianity – they took it from the pagans. That is just one example.