I think that they make a point to not show what their religious beliefs are. It's part of the personal/professional separation.

Not all of their clients will be the same religion. Not all of their clients would be accepting of someone who belongs to X religion. Religion might even be a trigger. So... some might choose to not disclose to any client (even if that client has the same religion) because word does get around and they wouldn't want to have another client learn of it.

Like... I'm an athiest. I don't particularly talk about my beliefs (or lack thereof), but I do instantly fear the judging that comes from people who are quite religious. It doesn't mean that they'll be like that - I just worry about it the moment I open my mouth. So if I knew the religious background of my T, I wouldn't go to see them out of that worry. I would have to know someone for quite a while before I'd be alright with that.