The American signatories were styled as citizens of the United States, while other delegations carried ranks and titles. That wording distinguished the republic from states with systems of knighthoods and nobility. An ordinary citizen could not commit the country to a treaty simply by signing it. The chosen representatives still exercised official authority, whatever form their description took.
Notable Point · 1:19-2:28
American citizens and the authority to sign a treaty
Calling the American delegates citizens expressed a republican identity while leaving their official treaty-making authority intact.