Welcome to the board from Southern California.
I sign every quilt I make that goes out the door. I have an embroidery machine and so use it to embroider on labels to sew on the back of the quilt.
I used to write on an extra block with a pigma pen and sew it on before I had the embroidery capabilities. Someone on here mentioned that they actually incorporate the signature block into the backing of the quilt so that it cannot be removed. I may try to start doing that.