I've been doing a bit more digging, and the general conclusion appears to be that either a profession has a specific requirement, usually postgraduate but not always (I think engineers may qualify as graduates at least), and if not then it depends more what someone does with their first degree than the actual qualifications beyond or otherwise.
Therefore someone with a degree in the humanities who goes into a job requiring that skill, whether academic or practical, they would normally be referred to by that status. I know the German system is the most specific in the world, where each profession is both regulated and part of your name as well as the extra letters (eg Herr engineer Schmidt etc), but otherwise does seem to be an informal designation based on a combination of your first degree and the fact you use it professionally. So if it's economics and you go straight into a firm of brokers doing analysis, do well and get promoted as a top advisor, I would guess they have as much right to be called an economist as anyone with a masters or above.
As these are only observations I'll put them out and see if they can be confirmed or contradicted.
Does the brain create or receive consciousness?