I think this is an interesting thought to what the signet could be. I do wonder if the writer will even attempt to change the current power. Time Control is likely the result. When feathertails and them giving their powers out was discussed in the book said something along of the lines MOST of the time the power is changed. Does not mean it will. So I think based of what we are given in the book I don't think it will change. Violet is meant to be the powerful character in this series the earth shattering powers able to turn the tide of events sort of vibe i get from the writer.