Horn or light signals are not very common unless something goes wrong. But they are very easy to learn as there really are only a couple you need to understand in those stressful situations.
5 Blasts is probably the most important, which simply means “I don’t understand your intentions” or more accurately in the real world “GET OUT OF THE WAY”.
The other night, during a rather nasty storm in a harbour, whilst boats were dragging everywhere and some had to resort to motoring for hours, around in circles, as their anchors would simply not hold, a Superyacht was obviously feeling extremely vulnerable and exposed.
Whenever one of these poor yachts came within 100m of it there was a very loud 5 blasts on the horn from the SuperYacht. It would have been nice I guess if everyone could have responded with 1, 2 or maybe even 3 (“We’re reversing”) blasts back that might have calmed the nerves of crew looking after a multimillion dollar investment.
But alas, small yachts are often not equipped with fog horns, other than the handheld variety and digging out such a device in the middle of 40+ kt winds might mean leaving the helm for too long. But at least most of these captains were able to keep a calm head and calm hand on the helm.