There are some free downloads of quilt labels on the internet.
I usually forget to label mine.

I should have said free "machine enbroidery" downloads above.

I put the label on after quilting because I am afraid it will not come out straight and where I want it if done before. As another said, a lot of time I use a marker and write it on a light colored back. I think it is very personal that way because it is in my hand. In fact I do that most of the time and even sometimes write a "For" for who ever is getting the quilt.

I have always sewn mine on by hand after completing the quilt, however, I have just finished quilting one and I am going to stitch it into one corner and hand stitch the other two sides. Should be quicker and will be more secure.