I knew that the band Wilco had used audio from a “numbers station” in some of its music long ago. The song, “Poor Places,” appeared on the album Yankee Hotel Foxtrot, which took its title from the source audio. Numbers stations were (and in some cases apparently still are) peculiar vestiges of Cold War times, simply voices sending out coded messages as sequences of spoken numbers, fully in public, usually on shortwave radio. Presuming the utilized code is strong enough, this information can exist out in the open, and be easily received by its intended audience, with no one else having any knowledge of what is actually being communicated.
This new video, from a YouTube channel called Ringway Manchester, runs through source numbers station audio that has been sampled on numerous music releases over the years. I had no idea this many songs had used numbers stations. And the comments below the video are full of additional examples and details (Thanks, Mark Rushton, for having shared this with me!)