signature campaigns will earn more points, as they are the best promotional campaigns. But if you have more points, you must join all campaigns
what points are you talking about? Do you mean activity points or merrits ? if that what you mean then yes signature campaigns will require some of them but that is not the op wanted to know because the op only wants to hear some strategy or techniques related to bounty ico campaigns.
Anyways , my own strategy when it comes to joining a bounty is i firstly check whether the manager that manages the campaign is trusted or reputable and i also check if the funds have been already escrowed or not.
by identifiying these two factors , i can know assure that those bounty are legit and will surely pay your efforts.