Disguise Spell( Song and Silence: A Guidebook to Bards and Rogues, p. 38)
You can cast spells without observers noticing.
Perform 12 ranks, Bardic music ability,
You have mastered the art of casting spells unobtrusively, mingling verbal and somatic components into your performances so skillfully that others rarely catch you in the act. Like a silent, stilled spell, a disguised spell can't be identifi ed through a Spellcraft check. Your performance is obvious to everyone in the vicinity, but the fact that you are casting a spell isn't. Unless the spell visibly emanates from you or observers have some other means of determining its source, they don't know where the effect came from. A disguised spell uses up a spell slot one level higher than the spell's actual level.