Signature campaigns are only a major source of Bitcoin for people who have accounts on Bitcointalk, typically have higher level accounts and are willing to spend time talking with other users on the forum.

The best ways to earn bitcoin are primarily through trading other altcoins back and forth and running a business that uses Bitcoin that you yourself own. it all comes down to what you are willing and able to do with what you have. For some people, a signature campaign is just starting capital.