That's in Arizona.
Here's a site that lists the individual states. It is for land surveyors but lists other occupations. Arizona is the only one I found that lists assayers.
http://www.libsci.sc.edu/bob/class/clis734/webguides/Russell_Liner_734.htm
I'm in Missouri and here are the regulated professions in that state. Assayers aren't listed. Strangely enough, neither are labs.
http://pr.mo.gov/regulated-professions.asp
I see nothing in the AZ document about operating over state lines. Can you provide something that says otherwise?
As far as I can see, there is no requirement for me to become certified. Also, for states that do require it, it seems to be related to the mining industry. I will only do assays on scrap and never on ores. No offense, but I had my fill of working with miners and prospectors many years ago.
I still can't find any U.S. laws governing the stamping of PM bars. Can you give more info on this?
Google has never heard of the Uniform Professional Code, except for accountants and actuaries.
I seriously doubt that anyone in any government agency is qualified to certify an assayer of PM scrap. Ore, maybe, but not scrap. Two different deals.
Canada seems to be a little more strict on all this stuff.