My Japanese skills are shit, but here's what I think it might (but very well might not) say... it's hard to read.

スイカわり

The second character seems to be an extra arch at the bottom, which I'm assuming is a fold or something in the hat... it wouldn't really make sense to me for it to be anything else. The last character り isn't clearly visible, but I'm guessing, without a clearer shot, that it's there, since it's the only logical completion of the rest of the string that I could find.

So... スイカわり (suikawari) is watermelon splitting - see toward the bottom of the page

Could be applicable... or not:

In Japan, suikawari is not much different, except that you have grown men wielding large sticks (bokken) while blindfolded and taking strikes at an innocent, expensive watery fruit. People crouch along the route to the watermelon, while others shout out guidance, both good and bad, to the blindfolded chump holding the bokken. One wrong swing and someone’ll get a bruise on his head or back or worse!