Seamus, regarding the above query about visual clues etc. I would say yes.

By first and last name I would be 95% correct.

By visual appearance and accent I would be 90% correct.

By accent alone - probaly close to 90% correct.

By visual appearance without the accent but knowing they came from Belfast I would be correct at least 70% of the time.

It's something we Belfast people cannot understand or even explain but it is true, and is probably true in other cities such as Derry and Armagh, maybe even Glasgow. I suppose we and our fathers before us have grown up with an air of suspicion all our lives that it has become second nature for people on both sides of the divide. I imagine that one would have to be from Belfast etc to develop this sense but to try to explain it is nigh impossible.
I am retired but work a few hours weekly in a retail hardware store here in Canada, I hear North of Ireland accents from customers quite often, and before they realize where I am from I instinctively know their religon , it's incanny because after talking to them for a few minutes my assumptions are correct about 90% of the time. In fact one time I heard this accent from an old man who came into the store, obviously from Belfast, I had him figured as a protestant from around the Shankill, but he turned out to be a catholic from the same street where I was born, we became friends after meeting a few times in a certain pub and I got to know him quite well only to find out later that he was indeed a protestant fom the Shankill who had converted to Catholicism when he married a women from my district. I told him what I had felt the first time I met him and he replied that he knew I was a catholic just by looking at me, so it's not all one sided.

I did have an interesting conversation with a gentleman from the West Indies about accents and he made a very profound statement. he said " you know Jim, we do not speak with accents but we hear with accents". I'm still trying to figure that one out.