if i don't use the computer to print a label i ALWAYS USE MICRON PIGMA PENS. they are made for this! they are acid free- archival quality- will not bleed or fade- made for writting on textiles.
and yes= i have on occassion written right on the quilt back for a label- i have also written an extensive label right with the quilting- so the label is across the top of the quilt...