This was 20 years ago. He was probably motorsailing down the middle of the shipping lane (he wasn't our best-informed or experienced partner). The Coast Guard gave him a warning for not flying the cone. It was probably a nice day, they were bored, and needed a reason to board a boat or two.
We've had an inverted cone aboard our boats ever since. When motorsailing in the presence of the Coast Guard, we'll hoist the cone in their honor {grin}.