Unseen Weapon (Su): As a standard action, you can wrap any melee weapon you wield in a layer of shifting shadows. This causes the weapon to darken, become less distinct, and leave a trail of shadow behind it as it moves. Your weapon must be in hand and ready to use for you to draw upon this power. You can dismiss the effect with a free action; dropping or sheathing the weapon also ends the effect.
It specifies "any melee weapon you wield" and "Your weapon must be in hand", and I think fists and feet are not able to accomplish those requisites, but just in case, it doesn’t hurt to ask.