Secretary of State and/or President can sign anything they want. Unless it's ratified by the Senate, it's paper suitable for use as a bar napkin. I wouldn't worry too much over it. Not saying there's no reason to keep an eye on them, but since Marbury v. Madison established the Constitution as the "supreme law of the land," any treaty would still have to take a backseat to it. Constitution/Second Amendment trumps a treaty.