Because the ruling is question resides over a piece of religious material Seeker.

It is a religious issue, but its merely a religious issue based on a loose interpretation of rules. There is no stated rule in their rules to say you cant do that.

The stated rule is:

Get into Religion/Politics or controversial topics unless you are a "Selectee". Anyone with over 30 posts can request to be added to this group. Once you are a Selectee, you will be able to see a Controversial Discussions forum that nobody else can see. In this forum, it is okay to post about religion and politics (this includes Bible verses and the like).

There are no other rules that state that what is in the signature was incorrect, yet any rule can be interpreted the way an admin wants to interpret it. One might infer that having something in your signature that is "forum-wide" is a violation of the above mentioned rule because it defies the idea that religion stay withing its own restricted area.