Secret Sign

You invisibly inscribe a small mark or short message (no more than 25 words) on a creature or object, similar to the way arcane mark works. The sign can be no more than 6 inches across, and if it's a written message, it can be in any language you can read and write at the time of the spell's casting. As you cast the spell, you can define one auditory, olfactory, tangible, or visual criterion--such as all creatures wearing green bands on their left arms or only creatures who smell of lavender or only orcs--that allows designated creatures within 30 feet to see the secret sign.

Disguises and illusions that mimic the set criterion can fool this spell. Normal darkness doesn't conceal a visual trigger, but magical darkness or invisibility does. Auditory criteria (such as a password) and tangible criteria (such as pressing your hand against a specific object or wall) can be performed by anyone who learns of them. A secret sign cannot distinguish alignment, level, Hit Dice, or class except by external garb, but can differentiate apparent races, genders, and garments. See invisibility and invisibility purge reveal the sign, but glitterdust does not.

A caster of at least 10th level can make secret sign permanent on an object with a permanency spell using 5,000 gp of diamond dust as a material component.