To pick the best signature campaign. You should have a a research on what ICO you want. Read their whutepaper and road map. What are the vision and goals of their protect. Also who is the teams behind of this project. Search also who is the bounty manager and her background.
Ill think to find a best signature is to research of it and work on it, Actually it was hard to find on which good signature that we need to participate. But just research ill know we find a best signature. And that's must to know more about the bounty manager also.