Finally found it! Super-genius me finally realized that, if I sent it in to the In Nomine list at some point, there would be an email of me sending it in. And lo! There was.
The Drum
This artifact is an extremely primitive drum apparently made out of wood, goatskin and animal sinew: one of the minor mysteries about it is why it still exists, as it seems to have been in use for at least two thousand years. It does not register as being Unbreakable, although it does register as an artifact. Merry Christmas!
The Drum has three major powers: one active, two passive. All powers only work for humans, which in this case includes Saints and Soldiers but does not include Undead. All powers also work automatically, with no Essence cost and/or disturbance; however, the user must be actively playing the drum for the active power to work.
The Drum’s active power is to generally interfere with demonic Interventions. Any attempt to summon a Prince (including Lilith) within normal earshot of the Drum (about one hundred yards) *reverses* any positive modifiers to the Invocation roll. For example, a Servitor of Theft who had the Lost Monet! (+6) and spent three Essence (+3) on the roll would actually be at -9 to the roll, instead of +9. This applies to -all- positive modifiers, and is cumulative with the first active power. Unfortunately, this power cannot be transmitted over any sort of communications media, although it cannot be drowned out by external sounds.
The Drum’s first passive power is to continuously interfere with a demon’s ability to do… well, anything. All rolls made by a demon who is within one yard of the Drum are at -10. The penalty decreases by 2 for every full doubling of distance: for example, a demon that was 8 yards away would be at -4, one who was 31 yards away would be at -2 and a demon at 32 yards and above would be under no penalty.
Needless to say, the Horde hates the Drum with a passion. The only really reliable way to detect the artifact’s special abilities is through observation and deduction, which can be a problem for demons, as this would naturally require Intelligence rolls. Still, the nature of the Drum can be eventually worked out, which leads to the second passive power:
Well, Someone’s keeping this artifact in one piece.