After Mal's ordinary brown shirt is transformed into brightly colored hawaiian print, he spins around to see the back of Lilly's after his eye catches something looking oddly like a skull.

"zhè shì shénme làn dōngxi? I mean, the skirt's shiny and whatever, but I ain't exactly been meanin' this when I said I wanted a shirt. Can you please change it?" Of course, the significance of this symbol completely escapes Mal's notice.