I put a label on every quilt. I generally use a fabric from the front. Sometimes copying a shape in the block, or from the quilting.
Example: Pinwheel block with leaves in the quilting. Made a leaf shape out one of the fabric from the front. Appliqued to the back. Another quilt had fish in the quilting, used a fish for the label.
I always include my name, who it's made for, and date completed. And if I have named the quilt, I'll add that, too. If it's quilted for you by someone else, you may wish to add that.
Sometimes, I add other little "doodlings" to the label. I try to make it as special as the quilt front, and unique to each quillt.