Every other method mentioned here either involves some kind of risk (gambling, trading) or low earnings (faucets,pay to click).
Signature campaign is an easiest and safest methods to earn bitcoins but you need to make sure that you follow the campaign rules or else you will be kicked out of the campaign and if you follow it then everything would be fine with you and apart from signature campaign there is a great demand for trading as most of the people are making good profits by trading altcoins though its bit risky but after learning it things would get easier for you in future.