I have to agree with smurphny, and add the following:
The danger/doubt signal (5 or more short and rapid blasts) could be used a LOT more. You may get a hand signal in response, but at least you've gotten their attention. And it puts you right with the Rules.
Inland Rule 25 (steaming cone) says "... a vessel of less than 12 meters in length is not required to exhibit the dayshape." Obviously that doesn't help outside the demarcation line
, but some never venture that far, or only motor when they're back in the harbor.
I cruise the Maine coast a lot, so I'm a big fan of automated fog signaling devices. More advanced radios
that have an external loud hailer come with this feature built in, but you can also buy a device that wires into your horn
circuit and issues the correct signals. Either way is MUCH better than trying to time it yourself and keep hitting the button. I find that most boats intentionally out in fog use their signals. The ones that got caught in fog unexpectedly, not so much. And of course those are the ones you worry about.
I know most small boats don't use maneuvering signals, but there are times when they are useful. Coming around a bend or out from behind a pier is a great time to give one prolonged blast. In states that require boater education, more and more people know the signals. In some (admittedly rare) cases it really can help two boaters figure out what the other is planning to do. And worst case, you can tell the admiralty court judge that you followed the rules, even if the other vessel didn't.