Like abs in general the 'V' (the space between your lower abdominal muscles and your hip bones) is made visible by lowering body fat level. Once your body fat level is low enough it will show and then can be enhanced by doing leg lifts, situps, etc to develop the lower abs and hip flexors. I like hanging (from a chin-up bar) leg lifts. You can start with knee ups, then progress to straight leg raises and later add weights to your ankles to increase the resistance.