you would see a "button" on the top of the mast. Round piece of wood like a flattish bun that would shed water. It might be wide enough to lead the halyard through for the "pig stick" that carries the yacht club burgee.
I learned about the button the morning after a thunderstorm in Ibiza. we'd been wakened by a big bang flash, but since everything seemed OK we went back to sleep. Next morning, I found a thin line hanging over the bulwark. Pulled it in, and half of the button was attached to it. That was the second strike on that mast and I believe the owner got a new one out of it from the insurance.