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.
By simply posting here in the forum. Bitcointalk.org. This is the site where you can earn bitcoin by joining in a signatur campaign. Quality post is needed for their campaign. You can earn btc if this signature campaign is successful and when the distribution given. If it is a token you can sell it to convert.