Combine balsamic vinegar and sugar in saucepan over medium heat. Bring to simmer, stirrring occasionally until sugar is dissolved. Remove from heat and set aside to cool. Arrange skewers starting with the watermelon squares, then basil leaf and finally tomato half. Repeat. Arrange skewers on plate and drizzle with the reserved balsamic syrup and olive oil. Sprinkle with salt. Serve.