Doctor Yellow is the nickname of a seven cars shinkansen train which runs several times a month to diagnose the shinkansen tracks. Since the Japan Railways companies aren't publishing the timetable of this test train, an urban legend was born among the railway fans, saying that spotting the Doctor Yellow shinkansen brings happiness and is a good fortune omen...
And, I may add that since the train usually passes very fast, it is quite hard to take a picture of it, too. I spotted Doctor Yellow several times, but I managed to take a good photo only once, in Kyoto...
Shinkansen Doctor Yellow, Kyoto EXIF info:
Nikon Df
Lens: 24-70mm F/2.8G
Focal Length: 70mm
Aperture: F/6.3
Shutter Speed: 1/2000s
ISO Sensitivity: ISO 400