If you fiddle around with a shortwave radio for a bit, you may stumble across an odd station that consists of weird noises or a mechanized voice reading out a long list of numbers. These are called "number stations," and they're believed to be the work of intelligence agencies. If an organization like the CIA, Knesset, or KGB has an agent within a country, a foolproof way of contacting them is through these signals because it's impossible for a government to trace who's listening in. And if you do dial in, only the spy could understand these string of numbers using a one-time pad. Literally all of New York City could tune into one signal tomorrow night and none of us would know who it's intended for and the meaning. Its height was during the Cold War, but it's still being used. In the US it's mostly for agents working for and against Cuba (although this may cease now that relations have normalized) and in the East around China.

Number stations follow a format. You turn on their frequency and they're (usually) silent for the whole day. Then at a pre-arranged time, usually at the top of the hour in the evening, suddenly something called the "interval signal" would come on for a few minutes. This is an old short-wave radio technique that allows the listener to fine tune the signal before the real broadcast starts. Then it's the header, which is usually a bunch of numbers, that people assume is a code for whom the message is intended for. After that is a noise to demonstrate the dispatch is about to begin, usually a series of beeps or even a voice saying "ready ready." After the voice will start spewing out the numbers, and this could last for a long time, maybe even forty minutes.

I sometimes wonder who designed these channels, particularly the interval signal, because they're so strange. Take this one. Who in room somewhere said, "Let's have a woman say 'Yankee hotel foxtrot' repeatedly. That's a good introduction to our code.'" Or the Lincolnshire Poacher, named after the song it plays. Why that crappy version of the song? Or the creepiest one of all, the famous gong channel that came out of East Germany? Did no one at the Stasi think, "Man, why would we put our agents through this? Isn't it pretty obvious they're listening to something crazy when people hear these loud gong noises coming from their room?"