Peel and dice the watermelon rind, ensuring no pink flesh remains.
In a large saucepan, combine vinegar, sugar, cinnamon stick, cloves, allspice, lemon slices, and a pinch of salt.
Bring the mixture to a boil, stirring until the sugar dissolves.
Add the watermelon rind, reduce heat, and simmer until the rind is translucent, approximately 45 minutes to 1 hour.
Remove from heat and let it cool to room temperature.
Transfer the pickles and liquid into clean, sterilized Mason jars.
Refrigerate for at least 24 hours before serving.