> Broadcasting in the open (i.e. not hiding the message) that Alice signed transaction X, unless Alice runs a business producing these transactions (i.e. Alice runs an exchange) - I am not seeing how that could be constructed as "commercial".

The only way this can be considered non-commercial is if both station licensees involved in communicating the transaction have no commercial or pecuniary interest in the transaction. When it comes to cryptocurrency, this is a pretty fine line to walk, frankly, as both stations have to be able to prove that they are not performing business transactions or processing transactions for some business-related purpose.

Also, amateur radio operators are expressly forbidden from broadcasting within the ham bands except in a few very narrow cases such as calling CQ to initiate a contact and operating a beacon. All other communications must two-way communications.

> Intent behind "non-commercial" I believe was to avoid businesses jumping on the free resource and completely saturating channel with business stuff

Quite the opposite. Early radio broadcasters and wireless telegraph companies at first opposed any kind of regulation of the spectrum for all the same reasons companies still do today. But once it was clear that regulated spectrum management was here to stay, they fought very hard to keep as much of it as they could for themselves. Thankfully the government at the time recognized that radio hobbyists continued to make valuable contributions to the science and art of radio and was able to create the amateur radio service only after promising the corporate interests that amateur radio would not interfere with their business models. That is, amateurs cannot broadcast or (with narrow exceptions) make one-way transmissions, nor can they use their license to conduct communications "which could be reasonably furnished alternatively through other radio services." I interpret this to mean that amateurs cannot use their license and spectrum to conduct personal business where a cell phone would do.

> With that intent in mind, P2P transactions are "non-commercial" in my opinion.

Part 97 actually doesn't say anything about commercial or non-commercial, it prohibits "Communications in which the station licensee or control operator has a pecuniary interest." I am not a lawyer and I do not play one on the radio but I would argue that if somebody is sending you money over the radio and the FCC took notice, they would probably ask you to prove that the money wasn't in exchange for some service, which would violate the pecuniary interest clause.

I have no relevant knowledge or experience, and also not a lawyer to discuss it in any more details. But just small correction for you and others who might follow: such broadcast does not imply that both sides are involved in the actual transfer of money. In general case they are involved in the propagation of the transaction, and direct payment between two HAM participants is just one of the possible uses.