[Varyon]

Power Ups 4: Enhancements has a Low Psychic Signature Enhancement, which applies to the use of special senses - -2 to detect it per +5%, matching with Low Signature, Variable (which gives -2 to detect with mundane senses per +5%). There doesn't appear to be a No Psychic Signature Enhancement... but that may just be because the authors of PU4 favored the Low Signature, Variable approach over No Signature.

My interpretation would be that the Low/No Signature Enhancements apply only to mundane senses, and you'll need to pay twice as much for this to also apply to special senses. Or you can pay normal price and still leave the ability perfectly audible/visible/whatever, but have the Low/No Signature only apply to special senses.