Small time artists and Native American silversmiths rarely trademark their work. The size or design of some pieces do not lend themselves to quality marking. Findings and components are often not quality stamped leaving the assembler the choice of attaching a mark, perhaps on a chain tab, to the finished piece. Many individual artists will stamp a quality mark along with their name or initials. While this satisfies the accountability at the heart of the US stamping act, it is not considered legal.
Some European countries DO require marking.
Many tourists in the US will question goods sold without quality markings. US Law requires a makers mark in the form of a hallmark or registered trademark in addition to the quality mark if the goods are quality marked.