If you want to earn Bitcoins without investment, then signature and social media campaigns are the easiest ways to earn Bitcoins. You can earn good amounts of money by participating in campaigns.
You can also work as a freelancer on various free lancer websites. You can work as a graphic designer or a translator and earn Bitcoins for completing the job given to you.
You can also earn Bitcoins from various Bitcoin faucets .Bitcoin faucets are a reward system, in the form of a website or app, that dispenses rewards in the form of a satoshi.