Earning bitcoin without investment is such an easy thing to do. Signature campaign is definitely the best way to do it. There are faucets, paid to clicks, micro tasks, etc. but those don't pay that much at all. It might pay a lot but only when you have thousands of active referrals. But that's not going to happen to most of us. Signature campaign is still the best.
You can also participate to bounty campaigns like twitter and facebook campaigns. After you have made enough money, you can try out trading. Trading is the next step towards making a lot of bitcoin. At first you will fail miserably but that's okay. Eventually you will learn how to trade right.
I see those who invented Faucets as slave drivers and advise people to stay away from them. Engaging in faucets to earn Bitcoin or altcoins is a gargantuan waste of time. Yes, one can earn through signature campaign without investment but it depends on ranking to make one's earning significant. Any earning below a Sr. Member rank is insignificant.