For PR practitioners, the issue of licensure has been around for a long time. Edward L. Bernays’ final years were spent hoping for some form of PR licensing to take hold in the US. Visit the Museum of Public Relations for a bit of background about Bernays’ work.
Also, from the PRbytes listserv (forgive me, I cannot find the originator of the post), there is an interesting download entitled: PR Measurement Comprehensive Overview.

Do You Need a License to Earn a Living? You Might Be Surprised at the Answer – …