Remember that sounds you hear outside of your spaceship aren't actually generated by the objects outside your ship, but are generated by your ship for the benefit of the pilot's awareness. So a horn could be made (a ship "beeps its horn", sending a signal to your ship that it interprets as "hooooonk!" or "beep beep" or "Get the heck outta da way!"). Jesus, such a thing would be so potentially annoying. People will follow others around honking constantly, which will lead otherwise law abiding pilots to lash out with "road rage" against the other annoying commander. Which, on the other hand, such notifications could be limited to one per minute or so. Like everything else I guess the usefulness of such a feature would depend on how its developed.
I'm not all for this idea, but if FD did it right it would at least be tolerable.