By using this spell, the wizard can create an invisible mark or rune on any surface. This mark remains invisible until conditions specified at the time of the casting are met. For example, the wizard could specify that the runes are only visible by the light of the moon or by the light of a moon of a certain phase (half, full, etc.), when viewed by an elf, at sunset or sunrise, when viewed by a wizard, when the caster is present, and so on. The spell cannot be used to transcribe magical runes, signs, glyphs, or symbols, but as many as seven letters or marks can be drawn. Unlike a magic mouth spell, a moon rune is permanent and will appear any time its conditions are met.
In addition to appearing when the proper conditions are met, a moon rune also becomes visible if a detect magic, detect invisibility, true seeing, or other such spell or effect is used on it. A read magic spell will reveal the maker's words, if any. Moon rune cannot be cast on a living creature. The mark cannot be dispelled, but it can be removed by the caster or by an erase spell.
A moon rune requires a special mixture of pigment including mithral filings or powder worth at least 100 gp.
Notes: Uncommon spell (PO:SM).