I had a lot of trouble with the signature thing too, but then I got it so I will help you out.
An easy way to do this is to register with mygamercards.net, there you can type in your gamertag and your language, then put the style. It will show you an example of what the gamercard will look like.
There are steps on that site that break it down pretty easily, so once you go there, it will be pretty simple.
If you have any questions you can send me a message