I attach after quilting and do it like hand applique. I prepare the label (I actually like to use the kind that are preprinted on fabric and cut like yardage) I cut out the pre printed label, starch it will (easier to write on that way) I write what I want with a pigma pen, turn under the raw edges, press and attach with hand applique stitch. Is that a whip stitch?
My machine also has a block alphabet and I have also used that to create labels. Sometimes I use a block that is on the front as a label if it is a "fancy" quilt.