I recently earned my credentials as a Certified Professional Ergonomist (CPE), and in the process learned that there's some lack of awareness and/or confusion regarding the certification options in the field of human factors and usability.
The CPE program is run by the independent Board of Certification in Professional Ergonomics. The certification covers a broad and deep range of topics including ergonomics, anthropometrics, interface design and human factors principles. Some companies and organizations have utilized CPE expertise to evidence the effective research behind the design of their products. For example, Microsoft advertises the role of certified professional ergonomists right on the packaging of the Microsoft Natural Ergonomic Keyboard 4000.
Without getting into a lot of detail, there are multiple levels of certification depending upon work and academic experience. Feel free to contact me if you're interested in finding out more about it.
To take a step back, the term professional certification refers to "a designation earned by a person to assure that he/she is qualified to perform a job or task" and "generally, need to be renewed periodically, or may be valid for a specific period of time (e.g. the life-time of the product upon which the individual is certified). As a part of a complete renewal of an individual's certification, it is common for the individual to show evidence of continual learning." Common professional certifications include accounting and nursing.
Many people in the usability field (particularly as it relates to Web and software user interface design) may be familiar with the Certified Usability Analyst (CUA) program developed by Human Factors International (HFI). Note that HFI is a company, not a professional organization, so the CUA certification is specific to HFI's practices and methods, rather than those agreed upon by an independent body (although HFI is considered an industry standard-bearer).
Moreover, the CUA is a relatively focused, short-term certification process "aimed at designers and developers who want solid training for practical work in user-centered design." In fact, HFI distinguishes between their program, referring to CUAs as "the certified paramedics of the field", in contrast with CPE credential's: "The CPE/CHFP program is aimed at full time usability engineering professionals. These people must have advanced degrees and at least four years of professional experience in the field. They are the certified physicians of the field."