I vaguely remember that in the Big Ask Keith Baker thread over at the WOTC boards, he said it was an essence node (basically, amulet-slot item that can only be used by warforged) that imparted the Blinding property to a warforged's built-in armor (despite it normally being a shield-only ability).
I also vaguely recall that the errata for the adventure changes it to a different item.
Yes, the Errata changed that to an Essence Node of Sneaking (or Scout or somesuch). It grants +5 to Hide and Move Silently, takes up the amulet slot and can only be worn by a warforged.
I decided to change it to something more interesting when I couldnt find it anywhere.
I havent fully figured it out yet, but so far when they have tried to pawn it off...no one has wanted it, but they readily ID it as a "Node of Essence" just no one is spilling what it does.
I like to keep my PCs guessing for awhile. 1/2 the fun is the "off-the-cuff" stuff anyway