Nystul’s Magic Aura

By means of this spell any one item of a weight of 50 g-p. per level of experience of the spell caster can be given an aura which will be noticed if detection of magic is exercised upon the object. 

If the object bearing the Nystul's Magic Aura is actually held by the creature detecting for a dweomer, he, she or it is entitled to a saving throw versus magic, and if this throw is successful, the creature knows that the aura has been placed to mislead the unwary. Otherwise, the aura is simply magical, but no amount of testing will reveal what the magic is. 

The component for this spell is a small square of silk which must be passed over the object to bear the aura,