If you log in to challenge.ootpdevelopments.com, go to your profile, and scroll all the way down, at the bottom of the page in bold it will say 'Signature.' Below that is an image similarly styled to the Perfect Team signatures. If you paste the link from that image into your signature, using the proper code around the link so it displays as an image, it might work.
Instructions on getting a perfect team signature are
here, and there is further instruction in the comments if you run into trouble.