RPGMemes

Conceal Spell

Through sheer mental effort, you can simplify the incantations and gestures needed to spellcast, leaving them barely noticeable. If the next action you use is to Cast a Spell, the spell gains the subtle trait, hiding the shining runes, sparks of magic, and other manifestations that would usually give away your spellcasting. The trait hides only the spell’s spellcasting actions and manifestations, not its effects, so an observer might still see a ray streak out from you or see you vanish into thin air.

Silent Spell (Metamagic)

Benefit: A silent spell can be cast with no verbal components. Spells without verbal components are not affected. A silent spell uses up a spell slot one level higher than the spell's actual level.

Doesn't work for Bard spells, although they have a way to disguise theirs:

Melodious Spell

You subtly weave your spellcasting into a performance. If the next action you use is to Cast a Spell, the spell gains the subtle trait, hiding the shining runes, sparks of magic, and other manifestations that would usually give away your spellcasting. The trait hides only the spell’s spellcasting actions and manifestations, not its effects, so an observer might still see a ray streak out from you or see you vanish into thin air.

There's always a feat for that!