It's exciting that you all care about your site so much you want to wear your allegiance. The only concern I had when I heard about this was "what would our pesky lawyers say?". As a rule, "It's easier to ask forgiveness than it is to get permission". That said, our VP of Community Growth says:
We do not object to your individual use of the logo in a personal and private manner.
Like, say for using the logo on a tee shirt you plan to wear yourself.
It gets a bit tricky when it comes to selling shirts. But as long as the charge is just to defray costs and it doesn't turn it into a business of some sort, I don't see any problem.
Unfortunately, we can't coordinate this event; y'all'll have to take care of that yourselves. You might have heard of our #SOreadytohelp contest. It took months to distribute the prizes and we've concluded its just not one our strengths. Sorry about that.