Have you ever tuned in to a number station?

Yes. Quite the find the first time tuning around. Always thought they'd died out with the Cold War.

Mysterious and fascinating find in the middle of the night. Not unlike getting some Morse, a Nav beacon, or even some jamming or OTH radar.

In my teens, I was a very keen short wave radio listener and that was one of phenomena that you came across while tuning. It took many years for me to find any information about them when the Internet became a great source of knowledge (as well as cobblers LOL).