A Quaker wedding is officiated by the Divine Presence (no priest!), and everyone present serves as a witness. A lovely tradition that has come out of this belief is the Quaker marriage certificate, signed by every guest at the wedding, even the kids. While the certificates were once very plain legal documents (Quakers used to view art with suspicion), today they are works of art hanging in every Quaker home.
And while it should go without saying, of course I'd be happy to make a certificate for a same sex wedding!