This will end up being the home for all of the information that we can find on the Lower Ward seeing as that appears to be our initial launch point, and I've been tasked to research it. That said, if anyone else has information that they think is relevant or useful, please post it here.
It's late at night for me, so I`ll add more to this in the coming days, but here are a few links to get us started.
Locations in Sigil (includes the Lower Ward): http://www.deathstar.org/~krlipka/ps/places/sigil/tsr-sigil.html
Maps of Sigil: http://www.shadowland.org/Planescape/maps.html
The Lady's Ward/The Lower Ward: http://www.shadowland.org/Planescape/images/lady2.jpg
The Lower Ward: http://www.shadowland.org/Planescape/images/lower.jpg
Drake
The Lower Ward used to be called the Prime Ward and was used as a ghetto for immigrants fromt he Prime to the city. This ended when the Shadow Sorcelled Key was used to open the portals to the Lower planes throughout the ward - resulting in the destruction of the place and renaming of the ward the Lower Ward. Of course the Primes were no longer locked in the ward after that either so maybe some good came of the carnage. Maybe.
Check the encyclopedia for more:
http://encyclopedia.planewalker.com