I believe that without signature campaign you probably could earn through the freelance work or offering goods and services, check the services section.
I believe too, how about you?, I don't know why so many of us don't do those jobs and accept small jobs aside from signature campaign... Actually signature campaigns now is being abused by those sig spammers and copiers even if it is easy to do this compared to other jobs that needs skills or attention..
Well signature campaigns is the most common way to earn money and doesnt require any technical skills to participate as long you are capable of making discussions and interact with everybody then it should be fine. Those skills that are commonly searched in services section are those skills which almost of us dont posses such attribute.