OK I had a play around for you and I don't know how the official ones off xbox.com work properly, so paste this into your sig this instead:
*url=http://profile.mygamercard.net/soldaat+t+1]*img]http://card.mygamercard.net/soldaat+t+1.png[/img][/url]
You just need to replace both the '*' with '['. I didn't put them in there because obviously that would've shown you the gamercard instead of the code you need to paste!
It'll look the same as the xbox.com one anyway, hope that helps!