A reward of �1,000 is being offered for information which leads to the arrest of people who sprayed graffiti on two trains at Leicester Station. The two three-carriage trains were withdrawn from service for two days for cleaning. The incident, at the weekend, cost Central Trains more than �30,000.
The firm said the vandals endangered their own lives spraying the trains.
Central Trains wants to boost security to stop more attacks, it says vandalism costs it more than �300,000 a year.
A spokesperson said graffiti is becoming a growing problem at Leicester station.