I was reading online the other day, and people were claiming that the bindi on a Hindu woman's forehead indicates marital status. I don't know why they think that; I've always read that the bindi represents the inner eye, focused on God.
It's true, it is the third eye, not marriage.
For marriage they use the red stuff (I think it is kum kum), and run it from the hairline up over the scalp.
The hair is parted in the middle so you can see it.
I was also told that the bindi is supposed to distract a man from looking lecherously at a woman.