🚀 go-pugleaf

[...]
->box you see in some stores) which takes voice input from the driver
->and displays messages out the rear window.  The display would fit into
->the rear shelf, and face upwards.  A piece of optically clear glass at
->a 45-degree angle reflects the messages out to the rear.  (This is to
->avoid obstructing your rear view.)
->
->Of course, you'd need some computer hardware to do this, and the
->vocabulary would be limited, but you could preprogram some common
->phrases like "Dim your lights", "Back Off!", "Your Turn Signal Is On",
->"You Turkey (or other appropriate epithet)".
->
->The other approach would be to limit your voice recognizer to the 26
->letters of the alphabet, space, and perhaps some punctuation, and then
->spell out your messages.  A combination of the two approaches would be
->ideal.
->
->If anyone actually wants to build one of these, I want credit for the
->idea and royalties.  8-)

  You are too late.  They already sell such a device (there is an
  mini  keyboard  near  the  dash) that feeds a rear-self message
  displayer.  Unfortunately (for you), I don't remember  where  I
  saw the ad and how much (it wasn't that cheap).  Oh, well.