By applying signaling theory to the strategies gangs and their prospective members adopt during the recruitment process, this article addresses one of the most crucial unanswered questions in the literature on street gangs: why, in any given pool of individuals with similar sociological profiles and motivations, do only some gain entry into gangs? Based upon two years of ethnographic fieldwork with gang members in London, UK, this article argues that gangs face a primary trust dilemma in their uncertainty over the quality of recruits. Given that none of the desirable trust-warranting properties for gang membership can be readily discovered from observation, gangs look for observable signs correlated with these properties. Gangs then face a secondary trust dilemma in their uncertainty over the reliability of signs because certain agents (e.g., police informants, rival gang members, and adventure seekers) might mimic them. Thus, gangs look for signs that are too costly for mimics to fake but affordable for the genuine article. This article thus demonstrates how gangs overcome their informational handicap ex ante by screening and selecting among prospective members based on “hard-to-fake” signals.