תיבת דואר נכנס - Dacollo

Hi David,
Yup, this character is used in both Chinese and Japanese, and it means "brain" (the big lump of meat and cholesterol inside our heads).
Have a great day,
Ian

PS: You're right, on the t-shirt, the small line between the two parts of the character is de trop: it doesn't belong there...
But a native speaker just filters it out as "noise" (vs. the "signal" of the character), so it's not really a problem as such...