I think it would be really cool if we were able to use a (simplified) flag semaphore system.
Flags would be items that can be equipped. Aside from the flag you would be able to fly on your ship, you would be able to hold that flag and move it around.
While the modern semaphore system uses two flags and is quite complex, I think just having one flag to wave around would be great for the game. The different 'signals' (positions in which you can hold the flag) don't really have to mean something. In this way, people can ascribe meaning to the signals themselves. Either by discussing a secret code, or by 'signalling conventions' naturally emerging over time.
What do you guys think?
I got this idea during a solo session. I saw a 2-man ship being chased by a Galleon in the night. I brought my boat around parallel to them and started turning my lantern on and off. The message I wanted to get across was "lets gang up on the Galleon". At first it didn't work and the small ship started shooting me, but when they noticed I didn't return fire it seemed they got the message. We, almost simultaneously turned our ship around and started to assault the Galleon. We all sunk in the end (including the Galleon) and it was one of most fun moments I had in the game! If we were able to use flags for signalling, this kind of communication can also happen during the daytime.