"Boys be ambitious" is kind of the catchphrase of Sapporo. It was a phrase coined by Williams S. Clarke, one of the people who established Hokkaido College of Agriculture (now Hokkaido University) and thus made Sapporo into a notable city. It's an incredibly famous phrase throughout Japan too, I've seen it used in puns and on merchandise in Tokyo, and in national newspaper articles that had nothing to do with Hokkaido at all. It's a pretty great phrase too, the full paragraph running:
"Boys, be ambitious. Be ambitious not for money or for selfish aggrandizement, not for that evanescent thing which men call fame. Be ambitious for that attainment of all that a man ought to be."
That's pretty bloody good advice.
Anyway, with the opening of the new hip-hop clothing store Chill In Da House Sapporo's urban trendsetters show that they too, keep Clark's words close to their hearts.