US companies will register to be on the Privacy Shield list and self-certify that they meet the high data protection standards set out by the arrangement. They will have to renew their registration every year.
The US Department of Commerce will monitor and actively verify that companies’ privacy policies are in line with the relevant Privacy Shield principles and readily available to the public.
However there are still ongoing cases about about the mass data collection by US government agencies as commented elsewhere on this blog.
The existing skepticism about the effectiveness of this agreement to protect the rights of EU citizens in not diminishing under the new administration: http://www.wired.co.uk/article/trump-privacy-shield-data