So I find myself wondering: How do you detect magic? Can a sorcerer detect magic cast in their vicinity? If so, how close? And what is the in-game explanation for this?

I would assume that sorcerers can "see" magical effects, which allow them to try to counter them, as per the rules in the book. Am I off-base with this assumption?

What about detecting things about spells that have already been cast? I actually had this come up in game, and had to cobble up something with Lx to do this, because it seemed reasonable that it could be done.

Please speak up with your opinions on these questions, and I'll respond tomorrow with how I we came up with a spell and how I'd rationalize it.

In the first game I played a gifted human, I was imprisoned and being held captive by a few people.. along comes my friend with his character after I led him there with my familiar. In either case he arrives at the shack I am in.. tied to a chair and gagged.

The seneschal made it so that I gave off a magical aura of some type that signaled to the other character that I possessed the ability to use magic.
You could say that the aura is given off by the constant flow of magical energies flowing through my character.. or something.

Either sorcerors can see magical effects in order to counter them, or they can identify the gestures being used to cast a specific spell or if the spell has verbal components.. can pick up off that in order to be able to counter.

Detecting spells that have already been casted is covered by the vision vagary: specifically the divination sub-vagary.
Page 107 states this: "Divination reveals the events of the past or possible events of the future. Divining the future only reveals the most probable event as the future is constantly rewritten. Vision heightens the mind's ability to represent or recreate reality through imagination. It does not alter the physiology of the eyes in any way. Vision is necessary in the creation of spells involving miniscule targets as well."

So there you have it.
-Ingenious