>>60785213
>without a decree by a government
That is my understanding as well. Whether they can be used as coinage is another question, even if very stupid to do so.
There was a story circulating about the one-kilo Queen's Beast Completer coin. Its face value is 500, and when silver dropped so low that face was more than content, a guy tried cashing his in and the banks refused it. Alas, I did not screen cap the postings (not from here), so I have to confess this is now just hearsay.