Meaning of "山区" on JR East station signs (Tokyo)

[Xiamen]

Hello,

 

I've always been curious about the "山区" often seen in the upper right of station signs.

 

I understand the the 区 means that the station is within the 23 special wards of Tokyo.

I've heard the 山 means it's on the Yamanote line, but I'm a little skeptical.  I believe the color of the box in the middle of the green stripe defines the line.  Also, the attached image has the "山区" but is for the Chuo line.

 

Thank you for any assistance.

[Socimi]

The " 区 " should mean that the station is in the "Yama-no-te" ( "piedmont" ) area of Tokyo.

The JR Yamanote Line takes the name from the area wich it serves.

 

 

[railsquid]

This is for ticketing purposes - long-distance tickets from central Tokyo are generally valid not from a particular station, but either to/from stations on/within the Yamanote Line (山),  for distances of (IIRC) 100-200km, or for longer distances, any station with the 23 "ku" (区). JR only, of course.