Nightscar

Nightscar was an illusion spell that put a mark on a creature or object that only the caster and those chosen by the caster could see.

Effects
If this spell was cast upon a person or creature, they had a chance to resist being marked even if they were unaware that they were targeted. If cast upon an object, or an individual that fails to resist, the target was scarred with a glow that could be seen in the dark. This mark lasted for a few days; even longer for more experienced wizards. The mark had to be placed on a visible surface or exposed piece of flesh, but could be cast from 30 yd (27.4 m) away. The scar remained visible through polymorphing, illusion, or invisibility.

Up to seven other beings could be granted the ability to see the nightscar, by being in contact with the wizard when the spell was cast. More conveniently, the wizard could hold up to seven small items (gems, seeds, stones, etc.) as the spell was cast, and then anyone holding one of those items could see the mark.

The scar could be removed by remove curse or dispel magic, but the presence of the scar was not detectable by detect magic or true seeing (since the mark was not really there). Detect invisible did reveal the mark to the caster of that spell.

Components
This spell could be cast silently with only gestures. The seven small objects were optional.

Realmslore
This spell was frequently used to keep track of thieves or persons of interest, allowed them to be followed easily at night even if they changed shape or disguise. The origin of nightscar was believed to be for tracking lycanthropes in their human form.