who the hell is baggiases
That's trim on the school building, the N we had to make into a Π because how the hell would you make it
what's hobbit day?
The 22nd of September (by Shire-reckoning), the birthday of both Bilbo and Frodo Baggins. Sometimes celebrated on the 12th since that's the Gregorian equivalent, but who the forget cares.
Did you/they get caught?
Perfectly legal. This is kind of a tradition. Often used to wish people happy birthdays, wishing luck to the home team on upcoming sporting events, asking girls to homecoming/prom, etc.
We also have a large boulder that sits about ten to twenty meters to the right of that particular message, that's painted to celebrate such things. Often a fence-cupping is accompanied by a corresponding rock-painting, but not always. This isn't so.
It's amazing to think how thick the layers of paint are on that rock by now.