Where are the rows with the black triangle above the window on the Boeing 737-900ER with the 20 First, 27 Comfort, and 133 Main configuration?

I did not notice any on my last flight. I want to see if any of you guys have seen where they are located, they are in or near the middle 1/3 of the plane, by the wings. But I dont know the exact row. I want to see it this time, and even though I wont sit in that row, I will look for it.