Some states "regulate" radon measurement & mitigation service providers and measurement devices by requiring registration, certification, or licensing.  Some of these states issue identification cards.   Call your state to learn more.  

You can also contact the National Environmental Health Association's (NEHA) National Radon Proficiency Program at 1-800-269-4174 (radonprog@aol.com) or, the National Radon Safety Board (NRSB) at 1-866-329-3474 (info@nrsb.org) for more information on radon proficiency.