The railway company apologised after services on the East Kilbride to Glasgow Central line were disrupted on Friday, January 9, following the incident.
It is understood the train which was scheduled to run on the line was stationed at an unidentified Glasgow depot when a perpetrator trespassed on the tracks to commit the act.
Subsequently the 7.47am service to East Kilbride and the 8.28am service to Glasgow Central were cancelled.
The line passes through Busby, Clarkston, Giffnock and Thornliebank.
A notification via Trainline. (Image: Trainline)
Passengers were notified of the incident on the station displays on the line and via the ScotRail app.
The British Transport Police say they have been notified of the vandalism and have launched an investigation.
Meanwhile, ScotRail bosses say they will continue to work with partners to “clamp down” on unacceptable behaviour.
Phil Campbell, ScotRail Customer Operations Director, said: “We’re sorry to customers who experienced disruption to their journey as a result of this incident.
“Vandalism of any kind has no place on Scotland’s Railway. Incidents of graffiti take up valuable cleaning time unnecessarily and those committing it put themselves at risk by trespassing on the railway.
“We continue to work with British Transport Police to clamp down on unacceptable behaviour and would ask our customers to contact BTP if they see anything suspicious.”
A British Transport Police spokesperson said: “Officers are investigating a report of graffiti to a train at a depot in Glasgow overnight from Thursday 8 January to Friday 9 January.
“Enquiries are ongoing and anyone with information is asked to contact British Transport Police by texting 61016 or calling 0800 405040 quoting reference 150 of 9 January.”