In terms of bitcoin earning signature campaign is the only way to get a steady income. At the same it also have its own risk with post quality and knowledge about bitcoin. At times you may get kicked from campaign which affects the earning. Trading also suggested which needs investment and the one with less risk is faucets but it won't give worthy income for the time you spend.
You are completely wrong on this that signature campaign are the only way to earn bitcoins infact its only a bonus and i dont consider it a permanent source as well.There are many ways like working as a freelancer here providing services can be much better for decent earning of bitcoins.