Cut the pink flesh from the watermelon. Refrigerate and save for another use. Using a vegetable peeler, remove the green peel from rind. Dice the rind. Measure 2 cups diced rind; place in a medium bowl.
Combine the water and pickling salt; pour over rind. Cover bowl refrigerate overnight. Pour the into a colander set in a sink; rinse under cold running water. Drain.
Place pickling spice on a double thick, 6-inch-square piece of 100% cotton cheesecloth. Bring corners together and tie with a clean string.
In a 4-quart Dutch oven kettle combine pickling spice bag, vinegar, sugar, and crushed red pepper. Bring to boiling, stirring to dissolve sugar. Stir in diced water melon rind, sweet peppers, onion and jalapeno. Return mixture to boiling. Reduce heat and simmer covered, over medium-low heat about 25 minutes or until rind is clear. Discard spice bag.
Pack relish and syrup into clean half-pint jars. Cover the loosely with flat lids. Allow to cool 30 minutes. Screw bands tightly and refrigerate relish at least 24 hours before serving. Store relish in refrigerator up to 1 month.