This started out as just a set of backgrounds; employed in the fashion offered by The 52 Pages. Which is to say, a single word - an Environment a character is familiar with, or a Profession or a field of Scholarly Study. Each category offers different sorts of advantage, though many are situational. There is not an exhaustive list of these, but enough are offered to demonstrate type.
So, in deciding how I would discuss the brief list below, a few questions had to be asked. Mainly, how diverse does one want to make the professions on offer? Does the DM offer Dragoon, Uhlan, Curaisser and Hussar - or just stick with Cavalryman? Some words do provide a clearly different application of strengths, however similar they might be (bonuses as a Legionnaire vs. bonuses as a Militiaman). Of course there will be a difference between the bonuses due to a Musketeer and a Hoplite - and the setting will bear some of the burden here. Unless one happens upon a world where the Spartans developed gunpowder. If you want to confuse everyone.
To some extent, this will rest on our own preconceptions. Sheriff will call up different images to Police Officer; just as Watchman may. Desert may conjure up the Sahara, or Australia, or the Mojave. The player must choose their own words, however much they may be guided in this.
Moreover, does each new background require an entirely new background? If it pleases a Player to be a Lictor rather than a Watchman, are you obligated to come up with a whole new set of advantages? I think not: they shall, more like, be much the same - until one comes across a certain set of situations when a Lictor might come into their own.
This should not discourage anyone from invention, however. A new set of words and ideas can push the shape of a setting and the encounters of a Campaign in interesting ways. When a Player says he has a connection to a Merchant house, it should not surprise them that a Merchant House becomes involved in the plot.
So: a few new background words, as they occurred to me:
Profession/Environment [Almost]: Borderer ...or (the oddly cool) Mosstrooper. This comes directly from the reivers of the Anglo-Scots border country - memorably detailed in the work of Sir Walter Scott and George McDonald Fraser's non-fiction outing The Steel Bonnets. The phenomenon died with the unifcation of the crowns. Though I hope that this Background could pertain to any relatively settled border between human states with a well-established relationship. This offers few Environmental benefits - except in the particular region of the border. Political geography does not always align with natural geography. Bonus might include a familiarity with rural crime, a clan network to refer to, a rough-and-ready notion of jurisdictions and horsemanship.
Profession: Signaller A military application: skilled in the use of flags, or drums, or the heliograph. The importance of communication on the battle field should be not be underestimated. Such a word might give bonuses to noticing a signal at a distance - or the patterns of that signal - or to decoding the signals of others. The possibility also exists to have Background Word: Bugler, which is much the same, but noisier.
Profession: Whitesmith Like a blacksmith, but for white metals - tin, often. More accustomed to work the metal cold and to do comparatively delicate work - rather than bashing out a horseshoe or plough. Bonuses much like another smith.
Profession: Millwright An engineer specialising in mills: working in wood and metal for the mill itself, quite possibly near a river or a millrace. Forget not a certain amount of stone working in installing a millstone. Quite nicely flavourful in a Medieval sense.
Profession: Sapper ...or Pioneer - though I have used pioneer elsewhere, and am loathe to use it again. Sapper fits the profession better, perhaps - Pioneer has too much 'Westward the Wagons' about it. Either way, it is again military. The sapper is concerned with the making and dismantling of fortifications; though the sapper is not a mason. Given that the player may not have the chance to make extensive use of a castle until domain level play, this may not matter.