The hair-over-one-eye design is a wardrobe-foreshadow marker. The which eye is covered will become meaningful at later points in the series:
Post-time-skip: the covered eye swaps to the right (an in-text design-evolution beat).
Whole Cake / Germa arc: the Vinsmoke lineage’s relationship to vision and to the hidden eye becomes thematically loaded.
Predictive use: any later panel where Sanji’s hair parts the wrong way or the covered eye is revealed is a load-bearing reveal-moment. The Ch. 48 introduction locks the default state of the wardrobe.
Note: Sanji’s hair-over-left-eye design is technically established as early as Ch. 43 (his name-card splash), but Ch. 48 is the chapter where the which-eye-is-covered detail is most-clearly load-bearing alongside the curly-spiral eyebrow.