I usually check with the charity about labels. I donate to one group that requests no "detachable" labels because of frequent washings in an industrial machine. In that case, I add the information to the binding or in a lower corner of the quilt back. This information can either be embroidered (before the quilting) or added by permanent fabric marker.
I also ask the charity what information they want (or not want) to be added to the marking. I have never had an organization say I can't put my name, city and state, date, reason for the donation, or pattern name. I do have one charity suggest that I only put my first initial and last name so that's what I do for them. Also (unlike this post), I try not to be too long-winded. For example, here is what I included on a quilt that I donated last week. J. Hubbard, Milan, OH, Log Cabin quilt, FTMC Children's Cancer Center, Donated 4/2012
Good luck and thanks for making donation quilts! I know someone will love them! :-)