It would be rare to find a lorry driver who can converse in English but most of them would know the words "Horn, OK, Please". Thye aren't obscure words and phone/smartphone is widespread in India with mostly latin script interface. So, while I agree that it has become kind of a protocol/decoration, drivers while knowing the meaning, wouldn't care much about it given that it doesn't hurt to write that and can potentially help.

> Of course you expect every passerby to steal your car and you act accordingly.

That would be an exaggeration. There hasn't been any vehicle theft in my wider social circle ever. I read news about capture vehice thieves and I wouldn't be careless about the vehicle but I wouldn't expect everyone around me as potential thief. May be things are different in TN.