You need to click on forum actions, then edit profile, and edit signature (probably other ways to do it as well). But I don't think your signature will be visible before you post a certain amount of posts (but I'm not sure).
Here is where you go to for information on signature requirements: http://forums.digitalpoint.com/faq.php?faq=signatures#faq_signature_requirements
But whats a fake sig? still cant get around how this thing is created its different from the other forums...
I think that a fake signature is what you put in the body of your message, above the line, and not at the bottom (in the signature form). For instance, you're allowed to sell using the signature form, but not in the post... unless it's on the business forums
You wont have the option to create your sig until you meet the requirements. Take a look here - you can add one afterwards. http://forums.digitalpoint.com/faq.php?faq=signatures#faq_signature_requirements