Joining a signature campaign is the safest and least risky choice, because it only makes quality posts and I will get paid every week.
and income after participating in a signature campaign is my addition to investing and I will develop a small part to trade, I am not interested in gambling or mining because I do not have expertise in that field and is risky for me.
I agree, one of the best way to earn here is through signature campaign. Just like what you have said you only need to follow the rules, make a quality post and exert an effort to be able to do it.
The only problem is some bounties dont pay in the end of their campaign or their coins are worthless. Its the risk that bounty hunters need to take thats why its important to do an extensive research before joining in a particular campaign.
On the other hand I find trading profitable as well but your profit depends on the movement of the market and the coins you're holding. It has risk thus its advisable to gain knowledge first before trying because its not easy as it seems.