Using a sharp peeler, remove and discard the exterior green portion of the watermelon rind. You should now have rind that is mostly white, with a little bit of pink and/or red on one side. Cut into 1-inch cubes.
Add the apple cider vinegar, water, sugar, ginger, salt, and spices to a 2-quart saucepan set over medium-high heat. Bring to a boil and hold for 1 minute, then carefully add the watermelon. Return to a boil and turn off the heat. Remove the pan from heat and cool for 30 minutes.
Move the pickles to a 2-quart jar using a canning funnel and ladle. Pour on as much of the pickling juice as possible. Cover the jar and leave at room temperature for another 1 1/2 hours.
Refrigerate overnight and consume within a month. These pickles must be refrigerated.