Because gold is valuable, there is no label, so the so-called label is unique, just like the license plate of a car. You can know whose car it is as soon as you check the license plate, and there is no label on the gold, so there is no way to check it. A gold seller, you need his ID card. This is to prevent him from selling you stolen goods. In case the police come to check, you will know who sold the gold. If you can't make it clear, you will be in trouble.