As for Politics and Religion, MiceChat only allows those discussions in the "Gold" section, which is limited to paid members 18 and older. Since your signature (no matter if you are a Gold Member or not) is visible to all, those topics are not allowed in any one's signature.
As for signatures in general, here is the question from the FAQ section...
The "Sig Line" is place where you can type a standard conclusion to your posts, or post a small picture or link to your personal web site. MiceChat does not allow you to link to other Disney Fan sites or post general advertising in your Sig Line - That would be considered SPAM and may result in the suspension of your account. While we do not have a "Maximum" size for signature images, users are asked to keep their Sig Lines as small as possible, so the boards do not become too cluttered looking. When in doubt, ask a Moderator for their thoughts and suggestions.
If you have any more questions, I strongly suggest contacting a Moderator.
One more section I highly recommend from the FAQ's...
Re: Warning Regarding Political/Religious images and text in Sig Lines and Threads
MiceChat has a general rule about keeping Politics and Religion off the main boards.
We are largely a Theme Park and Family Travel discussion board. Discussion of Politics
and Religion often result in anger, hostility, and don't promote the sort of topics that
we are actually focused on here at MiceChat.
We do allow discussion of these topics in our MiceChat Gold Debate Lounge. But I wouldn't recommend going there. As I mentioned above, those topics create anger and hostility, and you will find that in droves in our Debate Lounge. It is sad, but a prime example of why we don't allow such discussion on our main boards.
There are just some topics that are better left off of a vacation and theme park board