In signature campaigns, you pretty much put a message advertising something for the person who runs the campaign. Every campaign has its requirements. You can find a list of the campaigns available here:
https://bitcointalk.org/index.php?topic=615953.0Most of them require having a category of member of above, so you also need to post and participate in the forum in order to get that status.
Hope it helps.
Good tutorial. It depends on the company, while most companies pay altcoins, there is a select few companies that give bitcoin as payment when you join in their signature campaigns. Like the above-stated reply said, you would have to enroll or register, and you would need to post in the forum replying to many different topics or posting some queries or topics yourself. However, you should take note that most signature campaigns don't accept newbies, so the primary goal is to actually rank up your account, so you can have more projects to enroll in.