It seems rather odd that even modern automobiles--after all the years of trial and error--only have three possible visual signals (and only one audible signal) that they can give to other drivers. These are--I'm about to turn left; I'm about to turn right; and I'm braking. The audible signal--the horn--can mean anything from "hey, watch it!" to "hey, good looking!" It's about time some additional signals were added for all the things we need cars to do these days:
1) Letting a driver know you're letting them into your lane.
2) Letting a driver know they better not cut you off because you're speeding up.
3) Telling a driver to get the hell out of the left lane because they're going too slow.
4) Telling a driver there's a bicyclist being dragged under their car.
5) Telling a pedestrian that they must be jam 'cause jelly don't shake like that.
6) Telling other drivers that you'll be going slow for the next mile because you're not sure where your turn is and you're trying to read the signs which are poorly marked because the local authorities are mouth-breathing morons who should all be forced to find their way out of the South Bronx at 3 AM and see how they like it.