SpongeBob Planetarium Protest?

For several years now, during our live star talks at the Abrams Planetarium, some of us show a digistar picture of SpongeBob SquarePants over the stars of the Great Square of Pegasus. It gets a lot of laughs. Recently, (16 March 2006) someone placed this sign on our entrance door over night.

We removed it and the next day another copy was back. We're not really sure why. Does this protester not like the idea of us using SpongeBob in our star talks? Why? Could it be that someone is just trying to make a joke? I don't get it.
We haven't seen any signs since these two days. Does anyone have any clue? Has any other planetarium been a victim of a protest like this?