In the past, signals have been hidden by various means, including placing them next to a large signal such as an AM broadcast carrier or using spread spectrum technology to create low probability of detection (LPOD) signals. More recently the development of various digital modulation formats has provided a new means for signals to be hidden in plain sight. The presence of digitally modulated signals is commonplace now, to the point that if a signal looks familiar, such as a CDMA “Bart’s head,” it can easily be ignored as a known signal.