Conjurer: a branch, representing the class's favoured style of weapon (literally, a branch or twig with no embellishments), as well as referencing the lore of the class as using the powers of nature.
White Mage: a staff, perhaps referring to the Job's Relic Weapon the Thyrus which is of course a two-handed staff (the egg shape of the Soul Crystal also perhaps eludes to the Job's lore as a metaphor of 'giving life', and especially the Job's literal rebirth from obscurity)
Thaumaturge:this one is a little ambiguous, but to me it seems to be a flaming urn. This could possibly elude to the class's lore as their origins as funeral directors (their school of magic derived from spells they used in the preparation of the deceased, hence an urn).
Black Mage: a flaming meteor, which like the White Mage symbol refers to it's relic weapon the Stardust Rod, which was made from a fragment of a meteorite (also traditionally Meteor is regarded as the ultimate Black Magic spell in the series)
Arcanist: another confusing and ambiguous symbol, to me it resembles what in past FF games has been called a 'celestial globe', but in the real world is known as an
orrery, a mechanical device used for charting the movements of the sun, stars, planets and other celestial objects across the sky. What connection this has to the ACN class is anyone's guess, but given the fact the class was meant to be in version 1.0, but dummied out like MSK, and in fact was apparently a totally different design to how it was implemented in ARR (it's unclear exactly how it was going to work but the belief is it was meant to use mechanical staves and lay moving traps in battle), it's possible the movement of the heavens probably was planned to connect with that. But whatever it is, it's unclear as to it's precise meaning in connection to the class. EDIT: adn after a bit more research, in hindsight I think a closer real-life equivalent for the ACN symbol is a
Armillary Sphere and not an orrery, although the two devices are similar, an Armillary Sphere is closer to the ACN symbol in design than an Orrery is.
Summoner: another ambiguious symbol, to me it represents the traditional series 'summoner's horn' which is the Job's AF headwear (and following on from that, as a horn is commonly used as an instrument to call or alert others, it's possible it could be a double meaning, a 'horn' referring to the 'calling' aspect of summoning an Egi).
Scholar: this one had me scratching my head. The best I came up with was it was meant to be a stylized representation of an open book, not only the 'weapon' type of the Job (as well as ACN and SMN), but also eluding to the 'learning' meaning of the Job's name. But nothing is known for certain.