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.
I am planning to start the first few layers in PLA natural. Then the middle layers in ABS white. Then the last few in PLA natural again. Hopefully this will prevent any ABS from leaching into my garden. I guess I should order some PLA white, but all I have is natural right now.