[Spooks] From The Guardian : "Juanita Castro, sister of Fidel and Raúl who worked with CIA, dies aged 90"

[Martin VE3OAT]

 From The Guardian newspaper, journalist Maria Antonieta Collins is 
quoted as saying :
"the CIA used her [Juanita Castro] to smuggle messages, documents and 
money back into Cuba hidden inside canned goods. They communicated 
with her via shortwave radio, playing a waltz and a song from the 
opera Madame Butterfly as signals that her handlers had a message for 
her".

Does anyone remember those transmissions?

https://www.theguardian.com/world/2023/dec/06/juanita-castro-dead-fidel-raul-sister-anti-communist