What is the ruling on seeking blessings from the black seed (Nigella sativa) to ward off envy and the evil eye by placing it on a baby's clothes, or a bride's, or in the pockets of successful individuals, and does this constitute shirk (polytheism)?

Treating with black seed is a means of healing from diseases, but it should not be used as an amulet or a hung Ruqyah, because this is an innovation (bid'ah) and minor shirk, based on the Prophet's (peace be upon him) saying: "Whoever hangs an amulet has committed shirk." If one believes that it has an effect independent of Allah Almighty, then that is major shirk.