Talking Points Memo's Brian Beutler plumbs the origins of the coin:
An American lawyer writing under the pseudonym Beowulf first explained the platinum coin concept in the comments section of a post titled “ Repeat After Me: The USA Does Not Have A ‘Greece Problem’,” written by Marshall Auerback and published on a blog called The Center of the Universe.
His comments caught the attention of other writers, including management consultant Joe Firestone (.pdf), who pressured him to expand on the idea. “He eventually just broke down and wrote something on it,” said Stephanie Kelton, an economics professor at the University of Missouri, Kansas City, and an early evangelist of the platinum coin model, in a telephone interview. Kelton is the creator and editor of a website on economic policy called New Economic Perspectives where Firestone and Auerback are both contributors.
“It’s a variation on a theme that many of us have been writing about for a long time,” Kelton said. “If you boil things down to who issues the currency, you can do it via the bank, or you can have the government do it. This goes way back in the academic literature. … Now it’s being referred to as the magic coin and a gimmick, and certainly it has that aspect to it — but this law basically says the U.S. currency can come from the U.S. government. That’s really all the coin is. It doesn’t do anything terribly scary from my perspective. It doesn’t have any danger economically.”