I first heard it in a facebook group. They were discussing about bitcoin. They even posted some links on were to earn bitcoin. Others posted their referral links, later did I know that the links they've posted was just a faucets sites and they can earn small amount of satoshi in their referrals.
I first heard about bitcoin through my classmates but I also heard about it in group chats. A friend of mine also sent me links which are faucet sites. I tried earning bitcoins there but I realize that the earnings are too small and getting your money is not guaranteed. And then someone told me about signature campaigns and since then I have been earning good from it I also join altcoin because there are greater profits in trading.