A man stripped off all his clothes and ran naked up and down the aisle of a train travelling between York and Middlesbrough.
The service on Friday, August 29 was packed with passengers when the man streaked through the carriage.
Officers from the British Transport Police (BTP) released this image of the man as part of their appeal for information.
“The man clearly thought this was fun and a joke,” said Detective Constable Wayne Green.
“In reality, this was completely unacceptable and inappropriate behaviour which was clearly distressing for many of the passengers on board what was a busy service.”
Det Con Green asked anyone who recognised the naked man to get in touch, adding: “If you are the man pictured I’d urge you to come forward and take responsibility for your actions.”