((Marcus is going to be let out, otherwise, I have a discontinuity with the events of the Tribunal. Or you have the problem of Marcus escaping from the Diedne/Giants and have to deal with those repercussions. I'll play it whichever way is more interesting to the troupe.))
(( The only term I can think of is "token of safe passage", so it's not a failure of English. Unless MY English is failing me, which has been known to happen.))
I'm thinking something like a visa, but I'm not sure English had a word for what you're describing...which is kind of surprising considering how much English just makes stuff up all the time 
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Tranquillina gets to the front of the Customs line at the Magic Realm terminal ... She's allowed in, although the frost giant agent confiscates her apple.
5 pawns each of vis is earned. It's pro forma vis, consistent with the forms of spells cast in this story.
The vis can be excised from the body, and Tranquillina is strangely not bothered by the vis, if she keeps it within her body.
Sorry, what's "pro forma vis" mean?
As for using the vis, I think it would be cool for Tranquillina to collect another 5 pawns on a second trip to the Realm sometime, and cash in the 10 pawns for the Harnessed Magic Virtue. Story possibilities?
(alternatively, someone can help me think of a suitable Flaw to balance Harnessed Magic with the 5 pawns she's already got.)
Form... Any form, not tequnique...
Imaginem then, I'm guessing, given Tranquillina's actions. (Too bad - Perdo would fit both the story that happened and also her desired use for it with Harnessed Magic.)
Jacques will be Herbum since he is repairing the wall.