A Spiritual Signature is a concept coined by Dr. Michael Sharp to describe the vibrational imprint that a monadic spark makes when it enters energy and creates a field. This vibrational imprint is, like the tone of your voice, the features of your face, or the lines on your finger tips, idiosyncratic. The particular quality and shape of the vibrational imprint is determined almost wholly by the qualities (or Identity) of the monadic consciousness making the vibrational imprint.
A simple thought experiment should make this clear.
Imagine you have in your hand a tuning fork. If you strike this tuning fork it causes a vibration in the air surrounding. This vibration is the "hum" that we hear. If you were to strike a tuning fork and place it in clear water, you would be able to see the vibrational imprint of the tuning fork. This is exactly what happens when monadic consciousness touches energy. Like the vibrating tuning fork, it makes an imprint on physical matter than can be detected either by training your physical sense or, hopefully in the near future, by developing scientific instrumentation sensitive enough to detect the "subtle" impact of consciousness on energy and matter.
The concept of spiritual signature is used in the context of "channeled" communication with the Fabric of Consciousness. When a disembodied monadic spark enters the energy field of an embodied consciousness (i.e., enters the physical space of the physical unit, it's presence creates a "vibration" in the existing energy field. This "vibration' can be easily detected by someone who has developed their sensitivity to such things and can be useful in identifying the source of channeled communications.
In the cases of psychosis, where ego boundaries break down and uncontrolled access to the fabric of consciouses ensues, individuals may sense spiritual signatures and may report interference in the systems of their physical unit. This claim should be taken seriously and not discounted as delusional. Appropriate treatment requires, among other things, recognition of the reality of external "influence," the rebuilding of egoic boundaries, and education into the controlled access to the fabric of consciousness.