If the effect isn't started, then sanctum spell doesn't trigger, and sanctum fireball remains a third level spell. You can stick the glyph in your sanctum, and when a small kitten wanders by it'll get hit by a fourth level sanctum fireball, or outside and a kobold will see a second level fireball.
By the way, spoiler or trim that shit in your sig. Your sig should never be three times longer than your post.
Sanctum Spell doesn't change the effect of the spell. It changes its level. The metamagic checks where it is "cast": "level 1 higher than its normal level if cast in your sanctum (see below), but if not cast in the sanctum, the spell has an effective spell level 1 lower than normal."
It is effectively a level - 1 spell outside of the Sanctum. This is then used to trick the Glyph Seal into accepting what is normally, but is not in this case, a third-level spell.
EDIT: to clarify, since it is at that point already cast, when activated it still comes out at level - 1, not at its regular level, or at level + 1.
As for the signature, I'd have appreciated if you could have at least feigned courtesy. No need to be rude. I wasn't aware it was that long. It runs on one line for me, though I had heard on small netbooks from a friend (who has a small netbook) that it runs onto a second line.