A covert communication technique based on the principle of signal overlay is presented here. This technique in its basic form involves a covert transmitter transmitting a message signal that is weak, in relation to, and shares the same frequency band as an existing cover signal. The fact that the two signals overlap in time as well as frequency renders ordinary signal detection techniques ineffective in detecting the presence of the covert signal. The covert receiver uses the empirical mode decomposition technique to extract the signal. This new communication technique is described and its performance studied in this paper.