https://en.m.wikipedia.org/wiki/Gabriele_Gast
> After agreeing to help, Gast very soon found herself sent on an intensive spycraft course, including hands-on training with the latest in covert communications equipment. She was given a Stasi code name, "Gisela", which came with a false passport and a new handbag, incorporating a well concealed secret compartment. Back home in Aachen, every Tuesday evening at the same time she tuned into a shortwave radio station from East Germany and carefully wrote down a long line of numbers, read out in a monotone, without further elaboration, by a "radio presenter". When she decrypted the messages from Schmidt she found some were instructions while others were simply encouraging love messages.
If you can read German, Werner Stiller, the Stasi agent who was involved in this story, wrote a detailed account in the following book: "Der Agent: Mein Leben in drei Geheimdiensten".
Also in German: https://www.youtube.com/watch?v=-vVYu2HaX10
An account in English from Werner Stiller's son: https://www.youtube.com/watch?v=Y30yDu7_JBU
Long story short, she and her son managed to get through one of the checkpoints into safety. Numbers stations were a key part of the plan because regular communications would have been impossible.
There's one example of how it was used. It's a little funny to me how the stations were quite mysterious to me, but they were just part of everyday life for others. A necessary chore.
Wish I had a link to the story. Heard it years ago. If this story rings a bell for anyone, and you have the link, I'd be forever grateful if you shared it. It stuck with me for not only being a good Cold War story, but also for the practical use of numbers stations.