Tune across your shortwave dial and eventually you will stumble on a broadcast something like this....1645 2397 …. 1645 2397 …. 1645 2397 repeated over and over seemingly forever. Sometimes the number sequence is related by a male voice sometimes by a female and in one instance by a child’s voice. The stations broadcast in English, Spanish, Chinese, and others. There are stations that use music as an introduction others a simple statement “ready” others nothing just numbers.
Altho called number stations not all broadcast numbers some broadcast words or names. There is a station in Russia (UVB-76) that just buzzes. Buzz …. buzz....buzz...the station known as the Buzzer has been broadcasting this same noise pattern for decades. If you Google “number station” or “UVB-76” you will find very interesting and mysterious information about this station and others.
Go to Youtube and search number Stations to hear samples... try the “Lincolnshire poacher” or UVB-76. some have been put to backdrops which will make your skin crawl. After listining to the station "the Swedish Rhapsody" you may never go to the ice cream truck again.
Next go to the “Conet Project” http://archive.org/details/ird059 several recordings here...
Next if anyone has any info or sources please let me know...I find it fascinating