The only safe way I know and the most people also using is doing signature campaigns, they are easy and risks free.
If you do other methods you mostly also need to risks things and invest some money.
Not only signature campaign is safe and low risk you can also doing some bounties in our altcoin section that can help you to earn more bitcoins just to collect altcoin and exchange them into bitcoin.
of course the signature campaign is a safe method, but it is not a method for growing bitcoin, while we discuss are methods to grow safely?