I know that for residents of Saudi, their religion is written on their iqama; I'm not sure if they still do this, but Muslims would have a certain coloured iqama and non-Muslims would have a different coloured one (not sure if each religion has it's own colour or not).
Muslims have a green iqama, non muslims have a red one. (guess the red represents hell? Or maybe the fact that their blood is halal to spill? Who knows..)