Dive is signed the natural way (acting out diving) or the symbolic way. To do the natural sign for dive, put your flat, dominant hand on top of your flat, non-dominant hand, then hold them together in front of your head as you proceed to duck and act out the starting motion of diving.
Otherwise, you can use your hands to represent the diving board and the person diving. Hold your non-dominant hand out flat, palm facing down, then with the two upright fingers of your dominant hand representing the diver "standing up" , make a jumping motion off the "board" as your dominant hand flies in a downward 'S' motion until in lands in the water and swims away.
Teach your baby or toddler the dive sign when they see kids or adults diving by the swimming pool, or off a low cliff at the beach.
Teach your child this sign in context, when you are relaxing by the pool or at the beach, or when your baby's storybook character is diving.