Most successful online communities employ professionals, sometimes called " community managers " , for a variety of tasks including onboarding new participants, mediating conflict, and policing unwanted behaviour. We interpret the activity of community managers as network design: they take action oriented at shaping the network of interactions in a way conducive to their community's goals. It follows that, if such action is successful, we should be able to detect its signature in the network itself. Growing networks where links are allocated by a preferential attachment mechanism are known to converge to networks displaying a power law degree distribution. Our main hypothesis is that managed online communities would deviate from the power law form; such deviation constitutes the signature of successful community management. Our secondary hypothesis is that said deviation happens in a predictable way, once community management practices are accounted for. We investigate the issue using empirical data on three small online communities and a computer model that simulates a widely used community management activity called onboarding. We find that the model produces in-degree distributions that systematically deviate from power law behavior for low-values of the in-degree; we then explore the implications and possible applications of the finding.