The earliest visual indicator of
cannabis plant sex comes in the form of “pre-flowers”, which develop between the fourth and sixth nodes of the plant.
Male pre-flowers appear as tiny, smooth, egg-shaped pollen sacs about three to four weeks after germination. Female pre-flowers emerge a little later, between four and six weeks after germination, in the form of small V-shaped pistils with white or pink hairs.
hope that helps - it's what i look for to rid any males from seed that show their face
f's have more of a tear shape, sometimes hard to tell