Traditionally on the little finger of your non dominant hand ie if right handed on your left little finger
Signet rings are traditionally worn on the little finger of the left hand.
To physically wear it it meant you could seal a document on behalf of the king to make it official. It also meant you were a trusted and loyal subject.
it used to be said that the ring finger had a vein that lead to the heart. :) <3
To show the love and fidelity that you have for your husband/wife.