I love that the Green line trains are made by a Japanese company that sounds a little naughty. Every time I get on one of the older trains the Kinki plaque just cracks me up (I think the newer trains are by Ansaldobreda). I thought maybe you'd find it amusing too - aren't homophones fun? (I suppose I'm just guessing that kinki and kinky are pronounced the same way; I really have no idea how the Japanese would say it.)
After doing a a quick Google search, I've discovered that Kinki is actually a region of Japan. I still think it sounds funny and I'm sure I'll continue to laugh every time I see their little logo on the train.