Wash the watermelon rind thoroughly, remove the green outer skin with a sharp knife, and cut the white rind into bite-sized cubes.
Place the rind pieces into a saucepan, cover with water, and simmer for about 10 minutes until slightly tender but still firm.
Drain the rind and allow it to cool while preparing the spiced pickling liquid.
Combine vinegar, water, sugar, cinnamon, cloves, ginger, salt, and peppercorns in a saucepan and heat gently until the sugar dissolves.
Place the watermelon rind pieces into clean glass jars, arranging them evenly while leaving space for the brine.
Pour the warm spiced vinegar mixture over the rind until all pieces are fully submerged.
Cool the jars before sealing and refrigerating, then wait at least two days before serving for the best sweet and tangy flavor.