All cars in East Japan Railway Co. trains will have "SOS" stickers that clearly pinpoint where emergency alarms are located.
JR East took the move after an incident last summer on the JR Hokuriku Line in which a man managed to rape a woman in a train because none of her fellow passengers alerted railway personnel.
Every train car has an emergency alarm either at the front or back near the link connecting with the next car. When the alarm is activated, it will alert the driver and conductor, who in newer trains can also talk to passengers, the company said.
The stickers with SOS in white letters against a red background will be posted on all of JR East's 12,000 passenger cars by the end of June.
"We discussed what we could do as a rail operator. There are passengers not aware of the existence of emergency alarms. By clearly highlighting their location, we want them to travel in peace," JR East said.
In April, the Osaka police arrested Takamitsu Uezono, 36, a demolition worker from Shiga Prefecture, on suspicion of assaulting a woman in an express train on the Hokuriku Line last August.
At the time of the assault, which occurred on the night of Aug. 3, 2006, many passengers in the same car of the Thunderbird express did not alert the conductor or try to restrain the man after he threatened them.
According to police, Uezono took a seat next to the 21-year-old victim and told her, "I'll kill you if you speak loud." The man also threatened other passengers in the car saying, "I'll stalk you if you report this to police."