Nice idea.. and been done (well close)
There are bicycle handlebars that blink and/or vibrate..
not for others, but as a navigation signal for the driver (GPS

)
The disadvantage of the proposed system will be..
NO ONE will ever use a turn signal ever again in the near future!
and here's why:
Say you are well capable of using that convenient placed lever, and do so on a regular basis...
Now your fancy new GPS provides turn signals, and you f* love it..
even easier that way, right?
So you happily let the automata signalica do all the work for you when ever you're using the GPS system.
Say you're going a for a trip to California this winter.. or since this is you.. Las Vegas!
So you start up your GPS, and drive a few thousand miles;
the first day you're back home you turn off your GPS (why use it.. it's your home town, right

)
And you turned off your habbit of using that tiny lever a few days ago already...
Okay, you remember that inconvenient habbit a few days later and everything's good (YOU THINK!!)..
until your next trip to unseen territiry with the GPS on...
the more you use it, the less likely it'll be you signal fellow road users where you'll be going.
Simply because the human body and mind is as lazy as it can be;
if there is a more convenient or "easier" way to "solve a problem"
that's what'll stick best to gray matter.
And.. since that fancy GPS is
doing something for you..
you'll also get a reward (dopamine) when you use it;
thus it'll stick even better to NOT
lever the heII out of those tiny yellow lights of yours.
A few months down the road, you can as well remove that lever completely.
Remember the days when everyone was able to do simple math in their heads?
then came the seventies and suddenly 20 times 50 needs a calculator.
Or when every car owner had a fair idea of reading a map?
Well, ask a twenty year old to go from White Settlement to Dallas; and see them asking google for directions!
Same thing basically...
'sid