The other day, we were discussing what, if anything, we would do if someone advertising their religion would happen to apply for a position in our lab, e.g. as a bachelor's or master's student. It would probably be fairly easy to reject the candidate on counts of incompetence if he/she were a creationist and came to the interview with, e.g., a t-shirt displaying that. Matters become more complicated when the candidate displays their religiosity more generally, e.g. by wearing a headscarf, a crucifix or other paraphernalia. Would it be politically correct (or even legally permitted) to ask the person about their religiosity (not their religion!) in order to find out if any unscientific thoughts would conflict with their general suitability as a candidate in your lab? Would it be more appropriate to point out that religion and other organized superstitions are routinely mocked in your lab to deter the candidate?

Luckily I'm not in a position to make such decisions right now, but the topic came up and we wondered what one would most appropriately do in such a case, trying to neither compromise on hiring standards nor making oneself iable for potential unpleasant reactions or even law suits.