Well, I'm the guy that voted 'nonexistent'.
Adventurer is not a recognized occupation in my homebrew world. To the inhabitants of Korrel, the word 'adventurer' means something like the modern word 'Tourist', and it calls up the image of a wealthy, lazy, dilettante often of what we would consider Bohemian preferences. To the extent that they have a job at all, it might be writing a chronicle of their travels in exotic lands that they plan to publish, but more often they are just wastrels spending funds on food, women, and wine. They travel because they are so jaded by ordinary pleasures that they risk the dangers and hardships of travel for no better reason than novelty. Most goodfolk would consider them insane. The PC's are basically never 'adventurers' by this definition of the word.
In JRR Tolkien's "The Lord of the Rings", the Took family is rumored to engage in these sorts of "adventures". When Bilbo Baggins actually has an adventure as we gamers would understand the word, he nonetheless frames that harrowing adventure as the sort of adventure his neighbors would be familiar with - "a hobbit holiday".
Instead, the PC's are not on an adventure - they are on a quest, and they are generally drawn from the questing classes - nobility that doesn't stand to inherit, knights errant, templars, inquisitors, gentlemen at arms, priests with divine commissions, and individuals on quests of enlightenment or attainment or even revenge, together with the guides, sages, mercenaries, servants, bodyguards, and so forth that are accompanying them and assisting in the quest.
Most often the party operates under a mercenary charter that gives them rights to go about on the highway armed. Sometimes they are operating under the auspices of a noble person, who has rights to keep armed retainers, and they carry such papers as identify them as the henchmen of that noble. Sometimes, and this particularly true later in the game, their are one or more members of the group that hold patents of nobility in their own right, and they can therefore extend their protection to the rest of the group. At least from a legal perspective, the group is then in the employ of the nobles in the party and is his or her servant, even if internally the party acts in a more democratic fashion with no recognized leader. Sometimes it is a bit of all three, as it certainly doesn't hurt to have multiple layers of legal security.
To the outside world, the PC's are not adventurers. Before the PC's have much renown, they tend to be viewed as dirty no good mercenaries, mere hired killers, greatly to be despised. But as the PC's complete deeds of heroic valor or vile infamy, then they tend to be viewed as heroes or villains or sometimes both depending on who is doing the viewing. By this point, the PC's are no longer viewed by common folk as having a job at all, and tend to - as with the aristocracy in general - be ennobled by the fact that they don't have to work for a living per se, but instead can engage in noble pursuits like slaying dragons, casting mighty spells, and saving heirs in distress. Of course, the old money in the setting will still tend to see them at this point as dirty no good mercenaries, mere hired killers, but at this point they are useful hired killers worth at least maintaining something like a cordial relationship with despite their baseborn origins.
The PC's tend to be if not exactly unique, then pretty darn close to it. One thing that tends to mark them as big darn heroes and chosen of the gods is that they tend to have very unique and diverse backgrounds. It's very rare to see people travelling together who aren't all of the same family, much less of different nations and races. People see a group of individuals from diverse races travelling together as friends, and the first thought they tend to have is, "I bet one of them is a Saint." And their second thought tends to be, "And that means trouble is coming, and I'm going to stay out of the way."
Often as not, the only group comparable to the PC's in this fashion is the antagonists - who likewise consider themselves on a quest and not adventurers. There are of course other factions out there - thieves and assassins guilds, merchant families, noble houses, secret societies, mercenary companies, and temples to name a few - and they can put together something that looks like an adventuring company to further their interests, but then they would just think of themselves as members of that organization with a job to do on behalf of that organization. There are also freelance professional duelists, monster slayers, exorcists, bounty hunters and so forth but they tend to work alone or with just an assistant or two. If the PC's are freelancers without a fixed loyalty, they may be the only freelance organization of that sort for hundreds of miles.
