Well, actually no one can answer that question yet.
This video shows that it did drop @ adria pre- 1.0.4: http://www.youtube.com/watch?v=QGPQVCuO7xE
Keep in mind that this was the old version of the ring and that this mob might not drop it anymore.
This video shows that it does drop in the sewers as of patch 1.0.4:
To now I have done two "100 Unexpected Alies Runs",
And about 60+ runs that contain:
[Quest Unexpected Alies]
-Sewers Of Caldeum
Lately I always stream when im looking for the ring as you can see here:
Some people get this ring in like a hundred runs, some get in running 40+ hours.
Until now im certain that every mob that is able to drop lvl 14-ish ring is able to drop this signet.
To end this post correctly, I would just advise to actually do the unexpected alies quest to get the champion mob kill.
To everyone interested in this ring,
Good luck on your quest to find this ring.
I guess this is the wrong thread becuase people don't know how long each run takes them. I am going to make a new thread but the new thread might be pontless becuase people will troll the thread or won't time themselves. Here is the link for the thread with results. I will be trying to get about 50 to 100 of the rings. http://us.battle.net/d3/en/forum/topic/6522503697#1