Hello Rozyjazz,
At this moment in time the signature does not support Rich text/ HTML input. You should be able to put all your information and you can type your URL in plain text and the email account you are sending it to can have the intelligence to work out that it needs to hyperlinked.
Although that does not answer your question, If you try shortening your Signature(for example take away the url) then going back to compose does your signature display correctly?
Cheers,
Harry