Well, it was a theoretical example... But in order to get into a top signature campaign, you'd have to:

• get rid of your red trust... Or at least have more green trust than red trust...
• make high-quality posts for a long, long time... In order to get in a top campaign, you'll need to be a senior (or higher) member with a consistent pattern of high-quality posts that are getting a fair share of merit
• after you get rid of your red trust, rise to a higher account level AND made hundreds (or even thousands) of high quality posts, you can apply to join one of the many signature campaigns... It's up to the campaign manager wether he accepts you or not tough... And usually, if the manager catches you spamming or scamming he'll kick you from the campaign without any payment