My 1968 Valiant 100 Overhaul begins. :)
Hey 68,
The easiest way to tell is the badges. I believe the signet package was mostly a trim option. The dash would be upgraded and it would say signet on it. I have a signet dash for my car that will probably go in sometime. Other than that Im not sure. Here is a link to a really good source to Valiants,
http://www.valiant.org/index.html