Moo
To put your name on your food in the staff refrigerator is usually a way to ensure that nobody takes your protein shake that you drink every day, or your daily dose of fruit with your apple a day to keep the doctor away. When you put your name on it, it should belong to you and nobody else will take it.
Someone in this office was bold enough to see the note and decide to express their feelings about how big the item was placed in the fridge. This is a little bit more than a small joke when you go as far as putting an entire toy cow in said fridge to poke fun at size of the milk that someone brought in. This is a push little too far!