You must have a valid trademark, either registered or with a pending application (using the application/serial number), from one of the participating countries. The Amazon Brand Registry will only be for the country where the trademark is registered. For example, to enroll in Amazon Brand registry for Amazon.com, you must have a trademark registered or applied for at the United States Patent and Trademark Office (USPTO). For Amazon.co.uk, the trademark must be registered by the Intellectual Property Office of the United Kingdom.
For the United States, to obtain the verification code before the registration is granted, you must first register on Seller Central as a seller.