three, hair ornament, short hair or fur radical (no. 59)
彡 centers on fine, flowing strands: short hair, fur, or a decorative hair ornament. The radical sense is the same visible shape used as a component in other characters.
彡 is a pictograph of fine, flowing strands, representing short hair or fur. The modern three-stroke form keeps that image clearly.
See the three diagonal strokes as fine strands of short hair or fur flowing together: 彡 is a hair ornament or short fur.
For サン, imagine three (三, さん) strands of hair forming the ornament: 三 -> サン, and those three strokes become the hair ornament.
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kanji "three" or "hair ornament" radical at right