The ways in which various groups use affordable Internet‐based tools to expand the scope and variety of their members is well documented. We focus on the means they develop for identifying “suitable” members. Drawing on signaling theory, we offer a framework for analyzing recruitment practices in a digital media environment. We demonstrate that despite the differences among groups, a common logic guiding filtering behavior is the search for cost‐discriminating signs of trustworthiness, that is, signals attesting to the candidates' characteristics that are too costly for mimics to fake, but affordable for the genuinely trustworthy recruit. Focusing on collective action organizations, we propose a typology of organizations and trace the filtering tactics they develop for identifying members who manifest desired attributes.