Rail Fence works well for people to sign. And it would be space for larger prints to be used. Use 2.5" strips, 6.5" long: 2 strips of fabric of interest to your husband, with a white or muslin strip in between. Iron the muslin strips to freezer paper. You can have the blocks made ready to sign or just muslin strips backed with freezer paper available for signing. Any gel pen works for signing. Just mark off the seam allowance if you have just muslin strips.