Signature campaign is a good way to earn bitcoin.But, I don't think it's fast. So, If you wanna earn btc fast you should try altcoin investment. Altcoin is the best way for earning bitcoin.But you need to have skills and bit of luck.With all these you can earn btc fast.
Compared to any other available methods, signature campaigns are reasonably faster method to earn bitcoin in part time itself. Maybe if you are working in freelance site as a full timer, you might get some chances to earn bitcoins faster than signature campaign payments.
Usually the fast methods of not good paying, example: faucets. But signature campaigns are reasonably fast (weekly payments) and definitely high valued for the efforts.