If a female plant isn't able to pollinate it is likely to produce a lot of resin meant for making the cannabis seeds. A swollen seed pod with the pistils and THC laden resin is likely to turn a shade of orange and red and pull back inside the pod. The plant is then at the point of being harvested.
A cannabis seed isn't an element of the bud once the flowers reach the maturing stage. This is known by the term feminized, which means there aren't any seeds present.