Can a reference be provided from the Bible or other ancient Judeo-Christian writings that mentions the Seal of Prophethood between the shoulders of Prophet Muhammad, as a sign of his truthfulness and prophethood?

Among the proofs of the Prophet's prophethood, peace and blessings be upon him, is the Seal of Prophethood between his shoulders, which the People of the Book recognized him by, as in the story of Salman al-Farsi's conversion to Islam.

The absence of this sign in the books of the People of the Book today does not invalidate the authenticity of these reports, due to the distortion of their scriptures; they concealed what they knew of the truth.

Shaykh al-Islam Ibn Taymiyyah transmitted what refers to the Seal of Prophethood from the books of the People of the Book, such as the saying of Isaiah: "For unto us a child is born... and the government shall be upon his shoulder and between his shoulders"; he described him by his most specific and clearest signs, which is the mole.

Our advice is that you devote your efforts to gaining deep understanding of the Qur'an and Sunnah, for the texts of revelation are the path to guidance and healing for what is in the hearts.