Action Zone

You create a magical zone that reveals those who have committed an action that you specify. You create a 25 foot radius sphere created on a point of your choice within range. Until the spell ends, a creature that enters the spell's area for the first time on a turn or starts its turn there must make a Charisma saving throw. On a failed save, and if they have actually committed your stated action, a visible and dim light emitting a scarlet letter, beginning with the letter of the language of your choice that starts the word of your action appears on their body in a random location and lasts for the rest of the day or until they take a long rest (for instance if choosing dwarf language, then whatever character begins the equivalent word for your chosen action in the dwarven language would be chosen). You know whether each creature succeeds or fails on its saving throw.

An affected creature is aware of the spell and who cast it. Such creatures do not inherently know the purpose or meaning behind the spell.