We need to elaborate on this two things, the campaign manager or organization may have to set their own requirement for considering a member to participate in their signature campaign, talking of karma, we have some people who have already received enough karma and were not that active to as at when they were in the past, we received karma because we have contributed well to a post, which i think the post history should be the reason why there should be acceptance into a signature campaign when a user is active, and giving a quality and consistent post.