It's very common for people to display brands that they want to be associated with. E.g., in fashion, you can't copyright a clothing design, which has led designers to sell plain T-Shirts that say "Ralph Lauren", "A&F", "Hugo Boss", etc. Wearing a Google shirt is saying, "Hey, please associate our tiny little start-up with Google!" It worked! And check out the press they're getting for rocking the boat via the existing eBay-Google flap.

Just to clarify - only one of us wore a Google shirt. My co-founder was wearing business attire, so only I was singled out by the security personnel at first.

We don't yet have our own shirts and our appearance at the convention was spontaneous (planned the night before). I wore my Google shirt because our product uses Google Checkout and I wanted to show support for it as I felt it was dealt an unfair blow by eBay.

I agree. Once they're there though, it's a little too late to kick them out and not expect fallout.