I think that pay attention would fall under the category of caution. There are some countries that use the cardinal system where yellow buoys are marked with black to indicate better passage, where the hazard is, etc, and if coming from one of those places the yellow buoys might confuse. In the BVI for instance there is a cardinal buoy up by the airport, and I know that a lot of captains from the us don't know what it means, they just pass it to port going west and forget about it.
There used to be a yellow buoy outside Cruz bay, and people from all over would go around it , regardless of where they were coming from or going to. It was there simply to indicate that you were entering a national park and would be fined for groundings. But people rounded it just the same.