from GrogTag:

Now you can use your dry erase marker on our awesome Keg and Carboy Labels, making it easier to keep track of your recipe-specific numbers right on your carboy or corny keg.  Perfect for those of us who have several beers on tap at a time, or a few different fermentations bubbling away in the closet, our Keg and Carboy Labels will help you recall all the important information at a glance.  Time to clean that carboy?  Killed the keg?  Simply wipe off the info and start again!