It's Casual Dress During Spring Training

This guy was spotted in the stands of the White Sox-Cubs spring training game yesterday, and though we're not quite ready for that kind of fierce crosstown rivalry business just yet — it's like trying to have an argument too early in the morning, before you've had your IV of coffee — we like the spirit of it, for March. But we're not quite sure what the shirt is supposed to mean. Which guy is the Cubs fan again?