The male – female auspicious symbols in Hinduism is known as Mithuna and from time immemorial it is connected to Shiva, the cosmic male and his Shakti, eternal feminine.
In ancient fertility rituals male-female pair used to copulate in the field to ensure bumper crop. Fertility of humans is transferred to nature and vice versa. Hence in Indian art male-female couple, Mithuna, in various stages of intimacy is considered auspicious.
All kinds of Tantric sadhanas are based on this principle.
Upanishads state that Ananda or bliss itself is Brahman, the supreme godhead. Coming together of male and female is ultimate symbol of bliss, hence of Brahman, the god of gods, Mahadeva.
Male and female together is the source of bliss or ananda for both physical and spiritual.