Historically, checking for circumcision was the surest way to determine who is a Jew or a Gentile. So does the plaque nailed to the cross by the Romans confirm that Jesus was circumcised?
We know that Jesus was circumcised because we are told that he was in the book of Luke:
Luke 2:21 KJV
As Jesus said to the Sadducees:
Matthew 22:29 KJV
The Covenant requiring circumcision was with Abraham, and the Jews are the descendants of Israel, but they are only one of the Nations descended from Abraham, others include the descendants of Ishmael, of Esau, and that includes most of the Arabian peninsula nations.