I would have liked to get into it more, but Jim has been pretty cagey about the details of how it works. I get the sense that the "sponsor" of the runes -- if that's really the right way to model it -- is the head of Monoc Securities, given his secret identity.
Gard keeps a box of small stone chits each with a rune inscribed on it. To use the spell the rune invokes, she must break the Chit (and according to the story she does have a limited number of each). So possibly you'd be looking at a variation of crafting potions. Where you'd have to prepare (or be given) the rune chits in advance.
The user scrawls a mystic rune in his own blood to invoke the effect of that Rune. With limitations such as, cannot be used to break the 4th law (The Norsemen and their gods where very much about freedom and bowing to noone. Norsemen didn't even bow to their gods, insted considering them equals. Even Odin himself could not outright order others around.), Cannot be used to thwart fate (Narrators call on what is or is not fated to happen).
And such compels as, must kill Giants or trolls, cannot back down from a fight or show cowardice of any kind, must seek revenge for fallen friends and family no matter the cost, etc.
If I recall correctly, Gard talks about certain runes taking days to fashion, and for at least one of them she required an exotic component.
Richard
That was the (Even Hand Spoiler)Bullet taken from a dead man (dead hero probably), and it was an extremely powerful one. Also, it was not that it took her especially long to inscribe the rune on it, but that she was unconscious for two weeks afterwards.
Anyways, i think it's an extreme example. More common rune magic would be a lot simpler.
All the rune magics we've seen (lightning-bolt in Small Favor, collapsing roof and 'routine disguise'
The two weeks of unconsciousness
I would not actually treat it mechanically like other sponsored magic; it's not something boosting spells you're casting like Hellfire or Soulfire, nor is it cast more-or-less like regular magic like Seelie/Unseelie Magic given to a Knight who's not previously a spellcaster.
Instead, I'd think it'd be something like
Rune Magic [-2???]
You can prepare Runes. Preparing a Rune is mechanically identical to preparing a thaumaturgic spell; the Complexity of the Rune is equal to the number of shifts of effect stored + 2 if it must be actively used, or shifts of effect + 4 if it is set to trigger on a pre-determined condition. The Rune stores a Spirit Evocation of the appropriate number of shifts; a character can incorporate a number of shifts equal to their Conviction with no extra cost - above that, the character takes a Mental Stress hit equal to the number of shifts above their Conviction.
The type of Evocation (block, attack, maneuver, counterspell) must be decided while the Rune is being crafted. If the Rune is to be set to trigger on a pre-determined conditions, all decisions (number of targets to affect with an attack, whether to use a shield as a block or Armor) must also be set at time of casting; if the Rune will be actively used, this is unnecessary.
The Rune must be inscribed on a physical object. If a Rune is set to trigger on its own, the trigger must be an obvious action performed within line of sight of where the rune is placed. If the Rune is used actively, it does not cost Mental Stress as casting a normal Evocation would. When the Rune is activated, it needs no control roll and (for attacks or maneuvers) uses the rune-maker's Discipline.
A character can have up to (what's an appropriate number?) in runes stored at any one time. Others may use Runes prepared by a character, but they still count against this total until used.
Example: Sigrun Gard (Great Lore) seeks to make a Rune that will launch a Weapon:8 magical bolt when anyone opens the locker the Rune is placed in. This is a Complexity 12 Rune, so she must make up 8 points of Complexity. When she has performed the appropriate preparation, her Fair Conviction means she takes a 6-stress Mental hit, requiring her to take a moderate consequence.
Gard attempts to make a Rune that the bearer can activate to provide a 4-shift veil against Awareness; the Complexity is 6. When she has made up 2 points by preparation, her Fair Conviction gives her a 2-stress Mental hit.
The important thing about whether this is sponsored magic or not is really where the power comes from. It doesn't matter who taught her, because mortals can teach each other "sponsored magic" (like in white night When daddy Raith teaches Genosa's wives a sponsored ritual. He's not the one with the power, but he did show them how to access it
The original topic of this post however is "What does Sponsored Magic: Runes look (and feel) like?" so perhaps we should think about that.