Do you think it's possible to link an effect in an item to the detection of a magus's sigil and what would be the base of this effect ?
I would like to create a "safe" that would only open with a CreoVim spell cast by a magus with a certain sigil.
You would have to design an Intellego effect to detect the sigil. That being said sigils can be faked and there is already a way one can define the allowed users of an item. See effect use on page 99 of thr Ars Magica book.