Signature campaigns cannot be considered as the major source for earning BTC because they are not jobs, but rewards.
You should understand that joining them still does not guarantee that you will get paid unless you fulfill their requirements, with that said, they should be done as a way of contribution and should not be made just to earn some coins.
I think that it is the only major leading source from where we can actually earn bitcoin
but i am not sure about trading
Selling goods/digital goods are sources of bitcoin/money. Do services like translations, design,video editting etc.
Know your strength and use it, avoid gambling if you can and never trust hyip to last forever.
Increasingly apparent downside with digital freelancing services (regardless of currency you get paid in) is that you will end up competing with guys from India. Not many westerners are willing or even able to to do good job for 4 dollars/hour.
I think that is understandable.