If you don't believe in sex before marriage how do you spot stigmata diaboli in advance of the wedding?

That would be a problem .However not knowing what stigmata diabili are would be a problem as well. Third nipples I would hope ones partner might mention in conversation prior to getting naked. In any case you can always ask for a viewing without having sexual intercourse. If I remember correctly Clinton did not have sexual intercourse with Monica Lewinski. So he said.