Thanks to those who have helped so far. Place another piece of mount board over the print, turn the iron to a very hot temp.
Some people seem to really like the spray adhesive as it is less expensive than some other options.
I guess the only real answer here is to try it yourself and see how it works for you. I understand it is the sign of a true amature. Professional photographers generally sign the mount board just under the print. Of course, you will need to cut the mat window large enough to make the signature visible once it is framed.