OH. I did know what "packing peanuts" were, but I didn't know that hatcheries mark them for you. Makes sense. I wonder what they use to mark them. I wanted to mark one of my baby chicks recently and really, really didn't want to use leg bands, so... I had a can of temporary haircolor spray (from Halloween) that I sprayed on a Q-tip and used to mark the top of his/her head. It stayed on longer than I thought it would, but definitely had to be re-applied.