ALWAYS! If you don't want to use a full label, make up your own "mark" that you put on your quilts and put it in the same place on all your work. I think it is really important to at least put the year that the quilt was finished on the quilt.
I make the raffle quilts for my church, and I put a label on the back telling that it was a church raffle quilt, the year, our location and the title of the pattern. Celebrate your work!