An opinion on US "professional engineers"
I assume this would cover most states, since in years past I've read guidelines from quite a few of the respective state government units assigned to such things (mostly Minnesota) -- details may vary:
"Professional Engineers" are necessary in US state transportation departments to design roads and bridges. I would also claim that the PE's would review each other's work and supervise the construction, inspection* and maintenance of said civil structures. (*And probably do the inspections themselves.)
In the 1960s, the Minnesota Department of Transportation (MnDOT) designed and built a certain bridge carrying a major freeway (motorway) over a major river (Interstate 35W over the Mississippi in Minneapolis; if you knew that already you may know where I'm going with this). I would attest a PE designed it, performed all the safety calculations, and other PEs reviewed the design and co-signed the blueprints. Certain thicknesses of various gusset plates where called for on the drawings, by design. And yet, whichever PE(s) was/were supervising construction did not verify the correct thickness was used in at least one location. And subsequent PEs involved with inspections and maintenance never caught the error in ~50 years. (Add in the politics that MnDOT didn't have proper funding for proper inspections, skipping some and reducing scope on others.)
And in 2007 the bridge came down. Hard.
Mistakes were made, and people DIED.
PEs are people too, and to err is human. Mistakes will be made, but the system is supposed to CATCH them. No, it doesn't help that the politics and finances reduced the opportunities to catch it, but it should have been caught BEFORE a single car crossed over.
THIS is why we have PEs: to address accountability. And yet, the system FAILED from Day One of that bridge's operating life.
The "PE" on anyone's business card means their mistakes can be catastrophic to others, and the testability of their mistakes is nigh impossible. It doesn't make them "SuperEngineer" incapable of error. And it doesn't make other "engineers" inferior, just not accountable to the general public for their results.
(Truth be told, it was a dumb bridge design anyway, without much, if any, redundancy / graceful degradation. But it was the best, or at least sufficient, for its time.)
And another thing...
Not letting anyone working in an engineering field refer to themselves occasional / casually as an "engineer" -- forcing them to name the field -- is akin to forcing doctors to always list their specialty and never just saying "I'm/He's/She's a doctor" at the next Christmas party. Or lawyers: I don't need to know criminal / civil / estate / family / etc. Doctor and lawyer and engineer and firefighter (regardless of truck/engine/squad) and mechanic (HVAC, car/truck, large truck, industrial plant, other) and secretary/admin. assistant (I don't care to whom or which department), blah blah blah. Let someone be generic once in a while.
My claims (and it's all on LinkedIn if you knew me):
Degrees: BS & MS, Electrical Engineering.
Career: over 12 years in a "mobility engineering" role/department that does not require a PE (but does involve the safety of strangers -- see my handle?).
Once took and passed the "Engineer-in-Training" exam en route to a PE title, but my career went elsewhere.
I participate in testing of my own work (and that of others) all the time. Our union driver/mechanics build prototypes on site and shake them out, all while under engineering supervision. We try to catch the design issues before the customer climbs inside, not after. (You can't say THAT for a bridge; you have to trust the PEs that it won't fail, period!)