I'm wondering –considering GRCon'21 has another Capture The Flag challenge– whether such signal-centric problems, which typically also involve a more "classical" infosec problems but do need contestants to apply their investigative mind to signal processing / SIGINT problems are subject of this SE site, too.
AFAIK CtF questions are basically only admissible if the asker doesn't ask us to solve the flag for them, and I don't know where exactly you'd want to draw the line on advising people that might have more of a signal processing background on infosec approaches.