You could put the signature square on top of a background square with a fusible. You can then top stitch the edge for raw edge appliqué but the edges will fray after washing. The other option would be to cover the signature square that is fused to a background square and cover it with bridal tulle. The bridal tulle will keep the square from fraying and you could do a line of quilting through the sandwich just around the outside of the fused square. Not ideal but the only option I can think of that would preserve the whole message.