I think many are forgetting that only Arcane Tricksters with the 'Ranged Legerdemain' ability is allowed to use Mage Hand to do things like pick someone's pocket and such. I would put disarming someone of a weapon (not in hand, put say slung over shoulder or sheathed) into this category. Otherwise you're shortchanging the Arcane Trickster's abilities. I can't check right now, but doesn't Mage Hand say unattended object? I would classify something on my person, even if not held in hand, as attended.