Thanks for the nice guide!
The format of the banner is the following:
[url=link to the validator page
The problem seems to be that when I enter this entire link in the signature bar, the part
is erased after hitting submit and only [url=link to the validator page
] is left behind.
So I get as signature litterally: [url=link to the validator page
(see signature of this post)
However when I add that link to a post, everthing is rendered perfectly. Very strange.