Hi
I don't use anything to label my cartons, since it's not regulated around here; or elsewise not enforced.
There is a BYC member that makes beautiful labels for your cartons. Her i.d. is ADozenGirlz. I'm sure there are others. Also, you can order cartons with labels or the labels themselves from an online store like www.eggcartons.com .
I ordered some great labels from someone on here, unfortunately I can't remember who--it's been so long.
Recently, I have started printing my own to go on the cartons of the eggs I sell.