That's what this project does. It does signing, just not encryption. I would argue that this is OK legally.

I understand. I’m suggesting we could allow actual encryption if the messages were also signed such that the sender and recipient (but not the content) were known.

Abuse would require two licensed amateurs to cooperate to break the law and use the bands for commercial purposes. It would be easier to investigate suspected abuse (compared to unsigned encrypted messages, but not cleartext messages, of course)

And how would you distinguish licensed users from unlicensed ones if the messages are encrypted?

Heck, the authorities have problems policing the bands even without having to deal with crypto.

Licensed amateurs would be required to register the public keys (not private keys, of course) they want to to sign messages on amateur bands.