Legal Tender Gold and Silver
Read more at https://www.upma.org/legal-tender-gold-silver/.
The link you post is a completely different thing. You can look at how their site evolved https://web.archive.org/web/20140701000000*/https://www.upma.org/ and more importantly how long it has been in its current incarnation.
It is either a government honeypot to catch vocal rebels or a not too bright attempt to circumvent taxes.
A few generations ago the govt enforced a price for gold that would only be sustainable with responsible government. So, a $5 gold piece had roughly a quarter ounce of gold. It was the same as trading $5 worth of gold dust or flakes.
When the great depression hit it became necessary to invigorate the economy beyond what could be produced honestly, so the government told people to turn in all their gold and from then on paper would be used as money. This tangent has gone to the extreme, to where it periodically becomes necessary, in the eyes of bureaucrats, to 'make examples' of people who don't play by the new rules.
The United States has such a vast criminal system, the percentage of innocent Americans in prison is higher that the percentage of guilty people in prison in many countries. In other words in America if you are innocent you have a greater chance of being convicted than a guilty person has in many other countries. This effort includes vast numbers of police trying to encourage all sorts of illegal activity so that an arrest can be made, and the type of person who would be attracted to your link is a favorite of the law enforcement predators.