In the original post of this thread, there is a link that opens a window.

In that window is a form. You enter your email. (The email that was entered into your profile in-game)
Then you enter the nickname you want to appear on the card, along with the color of the card you want.

Press the submit button, and a new page will load with your newly generated card.
There will be 3 text boxes underneath. One for direct link to the image, one in html, and one in bbc code.
If you want to display the card in your signature, use the bbc code text.