The harmful interference caused by rogue radios poses a serious threat to spectrum sharing ecosystems. One approach for mitigating this problem is to adopt an enforcement scheme that can be used by an enforcement entity (e.g., Federal Communications Commission’s Enforcement Bureau) to uniquely identify transmitters by authenticating their waveforms. In this approach, the enforcement entity that is authenticating the waveform is not the intended receiver, and hence it has to decode the authentication signal “blindly” with little or no knowledge of the transmission parameters. In real-world scenarios, an enforcement entity may need to cope with additional challenges, including poor signal strength of the received signals and simultaneous co-channel transmissions from multiple transmitters. In this paper, we propose a novel concept that effectively addresses some of these challenges, which we refer to as Crowd-sourced Blind Authentication of co-channel Transmitters (CBAT). We also present a concrete instantiation of this concept called FREquency offset Embedding for CBAT (FREE). Our results show that FREE enables the enforcement entity to blindly authenticate multiple co-channel transmitters with good accuracy by harnessing the power of crowd-sourcing.