Yeah same country.
Last time i read the rules, it was a legal offence to paint on a public property under [PREVENTION OF DEFACEMENT OF PROPERTY ACT, 1985 | India Code]
As far as graffiti which you might have seen on trains in india are of a theme for which the ministry of railways has given permission.
As far as old or abandoned trains are concerned, still one has no right to paint on it as its a public property which might be later scraped off or dont know what happens to them. But illegally one is trespassing the premises and damaging a public property.
If you can show me a written rule which allows a common citizen to graffiti on a train then i am fine. Otherwise it looks people are doing this illegally and somewhere on forum we are promoting this illegal work.