Triangulation of your signal would be the enforcement mechanism.
Discussion
They can't even stop cocain coming in through their own mail service. How are they going to stop math being transported over waves of light?
If you transmit without a call sign, expect same-day service for them them to come find you. Same thing for encrypted packet radio. War driving is a sport, Hams will do it for free to help out law enforcement, lol.
That said there's no harm in transmitting bitcoin transactions maybe? As long as it's not for commercial purposes
