A 22-year-old train enthusiast was jailed one year and six months by a Japan court on Oct 4 for accessing a locked crew train cabin while on East Japan Railway's Joban Line.
According to local media reports, the female passenger had entered the crew compartment using a duplicate key she bought at an online auction.
The self-confessed train enthusiast used the key to unlock the cabin door at about 11.20pm on July 8.
She then played with the windscreen wiper and stole a train ID number sign, reported Japanese news site SoraNews24.
She hid the sign, which costs about 2,000 yen (S$24.50), in the waistband of her trousers.
The woman was later identified through closed-circuit television footage from a security camera in the compartment. She was arrested for theft and violating operational laws.
The Chiba District Court heard that the woman carried out the brazen act, as she "liked the 115 number Joban Line train and wanted to have a piece of it for herself", SoraNews 24 reported.
The prosecution had called her actions selfish.
The Joban Line runs from Tokyo through to Chiba, Ibaraki and Fukushima prefectures before ending in Miyagi prefecture.
The East Japan Railway Company has yet to issue a statement on the case.