That turned out to be a circular wave of one flag overhead. The agreed-on signal to send back when you were ready to talk was a circular wave of two flags. Kids these days probably use walkie-talkies you can buy at the toy store, or maybe cellular phones. But I hope some of them are still waving flags the way we did 40 years ago, making up their own language. It's a great foundation for learning how computers talk to each other over the telephone.
Computers face the same difficulties our little band of adventurers surmounted.
They need to adopt a common signaling language, and they have to agree on a lot of other things. If they don't, they can't communicate. They start with some sort of connection. The connection we had as kids was visual. But computers need wires and electrons.