If the ice cream truck is playing music, it means they are out of ice cream.
A childhood belief about ice cream vans

others believed things like this
- My parents told me that when the ice cream van was playing music, it means he's run out of ice cream :(Anon
- I used to believe that if the ice cream truck was playing music, it had sold out of ice cream.— Deprived of ice cream
- I used to believe that the Ice Cream truck would only play music when it was out of ice cream. Thanks, Dad.Anon
- when i was a kid my mother told me that when the ice cream man was playing his music he was out of ice cream— Lynnzea
- I used to believe that when the ice cream man was playing his music, he had run out of ice cream— Katie
- My mum used to tell me when the ice-cream truck turned on his jingle, it meant they had run out of ice-cream!Anon