JimmyC is right about being able to tell is Protestant or Catholic from their speech.
It's nothing I've ever thought about or analyzed, but there must be clues in the speech pattern and possible body language which, though invisible to outsiders, can be detected by Belfast people.
As Jimmy says, it's not 100% accurate, but as near as dammit.

Interesting thought here, Jimmy, Cobra and Fibs: could you tell someone's religious persuasion without visual clues?
By just the voice alone? As in the accents in Freda's link above?

Seamus