Sweet pickled what? While planning food for a southern outdoor wedding reception I came across this recipe.  I was intrigued to say the least.  After all, this is something we throw away, something as kids we chucked in the woods, seeing who could throw the farthest.  Growing up watermelon was something we ate often.  My dad had a huge garden that promised lots of produce including watermelons.  My sister and I were once featured in a small town southern newspaper sitting next to an 18lb Congo watermelon my grandfather had grown.  We felt like movie stars.  So when I read that there is a use for this white and green stuff we usually chucked in the woods or threw in the compost  I had to try it.
The finished product is like candy!  I am not kidding.  a very soft but firm sweet tasting candy.  We tried it with BBQ pulled pork and hot dogs.  I also found it to be delicious wrapped in bacon and served as an appetizer.  So, my conclusion, Don't Ever Throw Away Watermelon Rind Again!
Here is the recipe I used:
Watermelon Rind Pickles    
Yields about 5oz jars     
1 large watermelon (about 7 pounds)   
3/4 cup salt   
2 quarts (2  trays) ice cubes   
9 cups sugar   
3 cups white vinegar  
1 tablespoon (about 48) whole cloves
1 tablespoon whole allspice
5 cinnamon  sticks, 3 inch pieces   
1 lemon, thinly sliced, with seeds removed
Make the brine by mixing the 3/4 cup salt with 3 quarts cold  water. Stir well.    
Trim the pink flesh and outer green skin  from thick watermelon rind. Cut into 1 inch squares or fancy shapes as  desired.  You only want the white portion.  Cover with the brine 
solution, add the  2  trays (2 quarts worth) of ice cubes.  Let stand 3 to 4 hours.    
Combine   whole cloves and allspice tied in a  cheesecloth or other clean, thin, white cloth.     
After the 3 to  4 hours has elapsed, drain and then rinse in cold water and drain  again.    
Cover the watermelon rind with cold water and cook  until almost fork tender, about 10 minutes (do not overcook).     
While   the watermelon rind is cooking, combine sugar, vinegar, water and the  seasoning mix bag in a large pot and boil for 5 minutes.    
Drain  the watermelon rind and add to the seasoned syrup solution (remove the  syrup from heat). Let the watermelon rind and seasoned syrup stand  overnight in the refrigerator.    
Heat the watermelon rind in  syrup by bringing it to a boil.  As soon as a boil is reached, turn down  the heat to cook slowly for 1 hour.     
Fill the jars loosely,  with 1/2 inch of headspace.  To each jar add 1 cinnamon  stick.    
Pour boiling cooking liquid into each packed  jar  
Use a ladle or pyrex measuring cup to carefully fill each  packed jar with the hot syrup solution, again allowing 1/2 inch  headspace. Remove air bubbles and adjust headspace if needed. Wipe rims  of jars with a dampened clean paper towel; adjust two-piece metal  canning lids.    
Process for 10 minutes.