Regulation A+ is technically an exemption from registration requirements. Although in practice it works closer to a fully registered offering. Just pointing it out because the Stacks tokens are not "registered".
Transfers can take place between users/peers and do not need to be registered. Trading in the US needs to be on a regulated securities exchange while the token is treated as a security. See our FAQ question on exchanges: https://stackstoken.com/faq/
Trading in international jurisdictions depend on appropriate local law.
Finally, this is decentralized open-source technology and Blockstack PBC cannot control activities on the network.