The glowing hand imprint on Bo's upper chest is Hades' hand mark. It is similar to a "property of" stamp.
Like an umbilical cord, it lets her father, Hades, feed off Bo and gain power from her.
When Leviathan saw the mark on Bo she demanded to know where she had gotten it and said that she had been searching for it for six hundred years. She told Bo that the mark was supposed to be hers but it had been kept from her. Leviathan ordered Bo to give the mark to her and they agreed to a game of riddles to determine the outcome. (Destiny’s Child).