[size=9](A thank you to Avi-mun for finding a reference for Luci's blade. You're the best~)[/size]
Each Archangel has a sword specifically tailored to them, no angel sword looks the same as another; i.e., no angel has the same sword as Lucifer, none have the flaming sword like Michael, etc. Their swords represent their authoritative standing in Heaven, the rank of angel much like the stars on a military officer's uniform.
This one, is Luci's:
[size=9](Photo credit and artist credit goes to Gypsfulvus on DA. Link can be found here
Approximately 1 foot long hilt and 3 feet long split blade, it packs a devastating punch. The metal used is known to the angels, forged only in Heaven (with exception now to Mynardi; Hell's weaponsmith) by a material one could never find in any other realm. It's the only metal that could kill an angel and demons don't stand a stand a chance.
Much like Michael's flaming blade, Lucifer's sword has it's own specialized property. He doesn't often let those know what it can do.