A natural magical “fingerprint” unique to each individual.
Arcane signatures passively imprint onto spells, wards, and arcane devices — often used to restrict access or tailor effects to a single person. Some magical items “remember” their bonded user through this signature. Powerful mages or magical entities can sometimes hide, alter, or forge these imprints, but doing so risks magical instability or feedback.
A signature is like a soulprint — often unseen, but unmistakable once attuned to.