One suggestion offered to me after getting back blocks that were signed too close to the margins is to use the blue painter's tape to mark the quilt.
Are you sending all the blocks in a group to be passed from person to person or sending to individuals? I would package the blocks in plastic bags and possibly put some cardboard in to stiffen the envelope.
Send some Pigma Micron pens along so that they get signed with the right pens. There are a couple signatures on the school signature quilt that I really question what pen was used (I traced over the questionable ones with a pigma pen so that if the child's signature fades, their name will still be there).
My signature quilt project is prominently featured in my blog right now.
http://quiltingcorgis.blogspot.com/
Cheers, K