I have made several double wedding ring quilts and had people sign the back - at one shower, I wasn't in the room with the quilt and people signed on the front. The bride loved it.
This particular quilt was made from scraps and fabrics that identified the donor - cats for the cat lover, baseball for the jock - the background was from a dress shirt from the accountant. Maybe your family could come up with identifying fabrics (or you could) and have them sign in the center of that field
kcama
I added a tiny piece of scrap left from making my own wedding dress and any other ones from related people - maybe you could get snippets of siblings wedding attire (from an inside seam or something).