Bounty campaigns, sigcamp, social media, blogs, and others. this is a form of promotion and marketing strategy of a project. I don't think the signature campaign really matters to increase the credibility of the ICO, because basically investors see the use case and how important the project will be in the future. Investors can not only see from the bounty, it needs serious research and analysis. But with the bounty, the project will be widely reached and targeted, namely crypto enthusiasts.