How can you require that people not post in certain areas of the website if you do not ask them to offically state their religious beliefs somewhere, such as in the profile?
Hum...What if you come to this site as an atheist, but become a Christian later? After all, isn't that what the General Apologetics forum is all about. Or vice versa.
A moderate could move one of your posts from the "Christian Only" forum because he/she read you proclaiming your atheism, but missed your conversion.
Honor system works well enough. I had a couple of posts deleted once because one of the mods thought I wasn't Christian, but I think that's been resolved.
Would a simple two sentence explaination of your beliefs be too much to ask? One can put what denomination they are in their profile, but it is not mandatory, and even if it was not all Christians would fit into a single denomination.