The Constitutional text states the signing date using Year of our Lord, which of course can only mean Jesus Christ. This was common among the Christian nations of Europe and the soon to be nation of the United States of America.
Constitution: Article VII:
The Constitution was completed and sent to the states for ratification "by the Unanimous Consent of the States present the Seventeenth Day of September in the Year of our Lord one thousand seven hundred and Eighty seven"
Benjamin Franklin credited God with influencing the Convention used to create the Constitution:
“I can hardly conceive a transaction of such monumentous importance.... without being in some degree influenced, guided, and governed by that omnipotent, omnipresent, and beneficient Ruler in whom all inferior spirits live and move and have their being.” (1788 - TRBF p343)