A very dated Cold War joke, a version of which I first heard in the 1980s.
The KGB trained a spy to plant in Wales. The researchers decided the name Jones would be inconspicuous so he was given forged papers, inserted into Wales by submarine and made his way to a small village where he could observe operations at RAF Valley.
Some months later a handler arrives in Wales to find out what intelligence had been gathered. He went to the address he had been given and knocked on the door.
The door opened and he was opened with a cheery "Good morning."
"Good morning," says the Russian. "Is your name Jones?"
"Jones, yes, that's me. Can I help you?"
The Russian hesitates, then says quietly "The sky is red at sunset."
"I beg your pardon?"
The Russian repeats quietly "The sky is red at sunset."
"Ah, I see," says the Welshman. "I'm Jones the Milk. You'll be looking for Jones the Spy. He lives next door."