In most cases within my experience the designer doesn't have to be licensed or certified unless the contract requires otherwise. However, almost always, the design is submitted to a professional engineer for review and approval.
CHGuilford

• Only a licensed engineer may prepare, sign and seal, and submit engineering plans and drawings to a public authority for approval, or seal engineering work for public and private clients.

• Licensure for individuals who wish to pursue a career as a consulting engineer or a private practitioner is not something that is merely desirable; it is a legal requirement for those who are in responsible charge of work, be they principals or employees.

• Licensure for engineers in government has become increasingly significant. Many federal, state, and municipal agencies require that certain governmental engineering positions, particularly those considered higher level and responsible positions, be filled only by licensed professional engineers.

• With the growing complexity and the increasing diversity of modern construction processes and techniques, the engineer in construction must readily be able to communicate and exchange ideas and views with other licensed design engineers.

• For those pursuing careers in industry, licensure has recently taken on increased meaning with heightened public attention concerning product safety, environmental issues, and design defects. Employees have found it advantageous to identify to the courts and the public those employees who have met at least a minimum level of competence.

• State engineering boards are increasingly seeking and obtaining the authority to impose civil penalties against unlicensed individuals who unlawfully engage in the practice of engineering.

To find out what the limitations are in each state go to http://www.ncees.org/fundamentals/licenseboard.shtml and then to the states engineering board's page and read the rules and regulations.

Hope this information helps.
Rich

Richard M. Beldyk, PE, NSPE, CWEng, CPE
Professional Engineer - Delaware 6788, Maine 9987, Maryland 26594, Michigan 6201048734, Ohio 66691, Oklahoma 20523, Pennsylvania PE061240, Virginia 37138
Registered Member - International Registry of Professional Engineers - Certificate IR101
AWS Certified Welding Engineer - Certificate 0009Eng
AFE Certified Plant Engineer - Certificate 4582