Finding a witness to sign your marriage license easy, any adult attendee will do. However, selecting whom to sign may be tricky. So many people have shared in your day, you want no one to feel slighted by your choice. Parents, the MOH, and the BM, or the balance of the bridal/wedding party are a perfect pool from which to draw.
Today I learned for the purpose of signing a marriage license in Utah, witnesses do not simply observe the couple signing the document. Rather, the witnesses need to (1) hear the couple say “I do”, as well as hear the proclamation, “I pronounce you husband and wife.”