To identify a ripe watermelon, there are two key characteristics to look for. Firstly, a ripe watermelon will feel heavy for its size when lifted, indicating a higher water content. Secondly, examine the watermelon for a yellow spot. This spot is the area on the watermelon that was resting on the ground during growth. If the field spot is white or pale green, it may indicate that the watermelon is underripe.