The date of the wedding in the middle block. Maybe photos of them in the corner blocks from childhood and the time they met and dated, and then the celestial designs in the other blocks. Or celestial in the corner blocks and photos in the center top, bottom and side blocks so they are surrounded by the sun, moon, starts etc???
Personally I wouldn't put any of baby related things in their wedding quilt, save that for the baby quilt.
Good luck and post it when you are done. We love pics!