it's not a secret actually ,If you browse the forum regularly you can surely find some ways to earn Bitcoin.Your earning amount depends on your skills,If you have some skills like trading, programming, development etc then you will be able to earn more than 0.1 BTC per week.Again, Without investment you can earn up to 0.1 BTC per week by joining a signature campaign.
You can earn 0.1 btc weekly from signature campaign only if you have multiple accounts, there is no campaign that will pay you that high amount of bitcoins so its not possible to earn with single account and if you have multiple accounts and if you keep on spamming then surely you would be banned by forum moderators.