Is circumcision a physical mark of ethnic or religious belonging? Yes, it is because certain religions enforce it. However, bearing a scar on private parts is a quite ineffective method of self-identification. Secret physical signs are pointless in distinguishing infidels except in some public baths. Far more obvious but harmless and painless wounds could be inflicted. Although circumcision indeed serves for group identification its main goal must be somewhere deeper. Yet religions must be acquainted with it.
Bible, Romans 2:28
In any case, a physical mark that affects emotion and mind is actually a spiritual mark. As far as foreskin is sensitive it is an organ of thinking. As far as it is an organ of pleasure it is a spiritual organ. The fact that foreskin is an important erogenous zone means that paedocircumcision leaves not merely a scar on the skin but more importantly it marks the soul. Therefore, circumcision is not only a physical external symbol of religious or ethnic identity but a mental distinctiveness at work.