what do you mean ...? must have merits so that they can participate in campaigns such as articles
With all due respect, your English is horrible and it's hard to understand what exactly it is that you're asking.
If you can't put anything in your signature space, you won't be able to participate in signature campaigns. Therefore, Jr. Members that got demoted to Newbies can no longer wear advertising (or anything) in their signature. The only way to overcome this is to either earn 1 merit and thus become a Jr. Member again, OR purchase a Copper membership.
I don't know what you mean by "campaigns such as articles". If you're a Newbie, I think you can still do the social media bounties (Facebook, Twitter, Youtube, blogging) because those don't require you to wear anything in your signature space on bitcointalk. Does that clarify anything?