Help!!!

I'm seeing a lot of people who are posting in threads, having the detail of their cars at the bottom of their message box, ie:

______

Hyundai Elantra GT - This.. and that... and this.. and that...


^(up there)
How do I do this? I want to have this on everytime I post. Not sure if I have to upgrade my membership or it's something in the settings.

Please Help!