There's no such thing as a visible unfertilized seed; the seed begins to form when fertilization takes place. You have a pollen source. It can be one of a few things: Hermaphrodite flower on a female, residual pollen from a previous grow, a male that you did not kill early enough, or even pollen from a neighbor's plant you don't know about. lol!
THe tiny green seed-like things are just immature seeds. Brown ones are mature, or close to it.