You create a written message of 50 words or fewer, or else an image, a drawing, or a similar diagram. The figment hangs invisible and obscured upon the target surface for the duration of the spell. Another casting of _geomessage_ is needed to cause the figment to arrange itself into the intended message.
When you cast the spell, you can choose to incorporate a passphrase into the spell. If you do so, the message is protected as if [_nondetection_](/spells/nondetection) had been cast on it for the full duration of the spell, though creatures that cast _geomessage_ on the surface and speak the passphrase ignore the [_nondetection_](/spells/nondetection) effect and cause the image to become visible until the caster speaks the passphrase again.
Without a passphrase, the message simply remains invisible to those who cast _geomessage_. Detection methods like [_detect magic_](/spells/detect-magic) and [_see invisibility_](/spells/see-invisibility) indicate the message’s presence but do not reveal its contents.