Until air-conditioned cars were introduced to Indian roads, the people who drove, usually stuck their hand out of the window when they were about to turn right & twirled their hand from the elbow for a left turn. In the absence of indicator lights, this was useful to the dudes on vehicles behind.
But with the advent of air-conditioned cars, the glass on windows had be up always, hence this sign was printed at the back of the cars to warn the dudes behind them.
But after zillions of years, some people still have it on their cars. A status symbol, maybe?!

As seen on old Fiat and Ambassador cars - Since rolling down window would let out the hard earned AC! Plus the underlying possibility of passing bus to take parts of your hand with it, thereby disabling you from ever using hand signals, even if you should, god forbit, switch to non AC car!

Slang for MSG or mono sodium glutamate.

Ajinomoto Co., Inc. is a Japanese company that produces food seasonings, cooking oils, foods, sweeteners, amino acids and pharmaceuticals. It is the world's largest producer of aspartame with a 40% market share.

The literal translation of Aji no Moto is “Essence of Taste,” used as a trademark for the company’s monosodium glutamate (MSG).As of Feb 2009, Ajinomoto produces around 33% of the world’s MSG.Its head office is located in Chūō, Tokyo.