That was a fantastic idea KW802, thank you.
I came on here today to ask how to do this, amazing that it was asked today already.
For the poster who asked this question, here is how i did it.
I went to
http://mygamercard.net/ and got the code for the sig' gamercard.
I then entered this as my new BB Code.
Title: Xbox Live Gamertag
Tag: XBL
Replacement: <a href="http://profile.mygamercard.net/{param}">
<img src="http://card.mygamercard.net/sig/{param}.jpg" border=0>
</a>
Example: [XBL]YourGamertag[/XBL]
And added a button.
It looks great.