I always add a label. Quilt Name, Recipient (if there is one), Date Completed, City and State. I usually use a 3.5" x 5" piece of muslin and hand write the info. I only use a Pigma pen.
I also keep a quilt "journal" where I record quilt info. Name of pattern, designer (if not one of my own designs), book/magazine/commercial pattern name, fabric manufacturer, fabric line name, colorway, and my thoughts as I construct the quilt. I include why I chose that particular pattern, color and fabric. What the occasion is that I am making the quilt for. Something about the person I am making the quilt for. Problems I've encountered as I make the quilt. Any changes I've made to the pattern. I include the actual information that I've put on the label to have a "permanent" record of the quilt. I also include a photo (or 2) of the finished quilt. A lot of work, but it is fun to look back over the quilts I've made over the years. I can "look at" the quilts I've given as gifts and still see them anytime I want.
Btw, the only shows I've entered are local, non-juried, guild shows. Labels required as well as short wirte-ups about the quilt (my journal comes in handy for this).