A brazen gang of vandals stopped a train at Otford station on Saturday morning so they could spraypaint a mural on the side of one of the carriages.
Police say the graffiti attack accorded in the early hours of Saturday.
At 12.39am a CityRail train from Sydney stopped at Otford station and, while it was waiting at the platform someone placed a milk crate and a piece of timber on the tracks so the train could not move.
A tree branch was also jammed into a door to stop it closing.
Then five people emerged from the shadows and began to spraypaint a mural on the side of the train, while the driver and passengers remained inside the carriages.
Five minutes later, the gang finished their work and ran off, just before police arrived on the scene.
A police dog was used in the search and tracked the offenders to a location where police believe they jumped into a waiting car and drove off.
Investigations by the Police Transport Command are continuing.