Couple Questions...

First is pretty simple.
Do I roll a die for damage and soak? I've (possibly erroneously) thought soak was a flat number and that improvements to damage were based entirely on attack...

A set of glasses that give a blind person sight. (Yes, I know glasses are technically an anachronism in 1220...not until the mid-late 1200s...just that's small peanuts compared to mages and faerie ;D)
I was thinking Intellegro Imaginem with a Mentem requisite giving the ability to process input delivered through the glasses.
Only problem I see so far is that I might be using the concept of species incorrectly...although the spells in InIm seem to suggest something like this is possible.

Finally, a little clarification on Sigils.

Correct. If the attack hits, add the damage modifier, subtract the soak. No further rolls required.

Intellego Imaginem should probably be sufficient -- otherwise Intellego spells would always require a Mentem requisite, otherwise you wouldn't ever be able to make sense of what you perceive. Even for a person that was blind from birth, the Mentem requirement seems to me a bit too much of a modern interpretation.

They are magus-specific special effects that accompany spell casting to add flavour to the game. They also linger in the magic traces of any spell even after it expires and can lead to identification of the caster (via Intellego magic), even if the "special effects" were only transient.

Finally, they also refer to the physical symbol used to represent a magus and his vote at tribunal. A magus can entrust his sigil to another to let him vote in his stead at tribunal.

So would they be visible while the spell was active even to mundanes? Like, say, someone's sigil is Mist, would a Creo Aquam spell meant to create drinkable water for a Moon, would the water give off constant mist if that was what the fella in charge felt was appropiate?