Long ago I had read that the Kolkata underground system was pride of the city. So, I checked the web to see if it was still like that (no spitting of pan, etc). To my surprise, the problem exists but not to the extent it happens on the buses, etc. Please see
Kolkata Metro Updates - Page 184 - SkyscraperCity
If you know who the culprits are making them clean up the mess and paint may deter them reoffending.
Have a nice day.
Simhan
A retired academic in the UK.