As a visible sign of a covenant with God, men were circumcised - Gen 17:11-14. Why wasn't there a more obvious sign of 'membership'? For example, why not have ears clipped? How often does a man show his penis to others? Wouldn't it be more visible if something else was marked?
Circumcision was meant to be a sign of God’s covenant with humans. Rooted in the understanding of humanity at the time was the idea that only males were fully human and that women, due to their gender, were not. Men, therefore, were to have the sign of the covenant performed on their penises, the obvious sign of their maleness. This naturally excluded women.
Why wasn’t there a more obvious sign of “membership,” such as having the ears clipped? Because that would have included women, and the males of the clan would not have allowed this to happen. Women did enter the covenantal relationship and were made participants of God’s blessings (cf. Gen 16:7-14; 17:15-16) but in an ancillary way, through their belonging to a kin group headed by a man (father, husband, brother), never on their own.
Therefore, circumcision, though a rite passed as a divine ordinance, had a clear male bias behind it, since only men could undergo it.