For the last two years I've been planting veggies in my garden and marking them Sharpie drawn signs. The Sharpie always comes off in the rain. These handy little signs should last forever. So far I have made cauliflower, kale, beets, broccoli, snap peas, cucumber, tomato, and peppers, blueberries, and spinach. Check out the customizer version derivative.
You can also register your Makerbot at Azavy to print these for people for money.
https://www.azavy.com/users/paulhoover/products