The World Egg is the product of Damballah Wedo (the father serpent) and Ayido Wedo (the mother serpent). These two Loa are amongst the most important in the Voodoo pantheon. Damballah Wedo is considered to be the father of all the other Loa, and along with his wife Ayido Wedo, to be the Loa of Creation. Ayido Wedo is the rainbow serpent, and is a Loa of fertility.
Therefore the World Egg represents new life, potential and beginnings (much like it's equivalent tarot card, the Fool). It is a motif found in the creation myths of many cultures and civilizations. Typically the World Egg is a beginning of some sort, and the universe or some primordial being comes into existence by "hatching" from the egg.
The symbolism of a snake and egg also appears in the Thoth tarot as the Orphic Egg (in The Lovers and The Hermit). In Ancient Greek mythology, from this egg hatched a primordial hermaphroditic deity who in turn created the other gods. The egg is often depicted with a serpent wound about it. The NOVT appears to be influenced by Thelemic principles, so perhaps the World Egg is a reflection of these ideas. Carrying this thought forward, Damballah and Ayido Wedo could therefore symbolise the Lovers in the Thoth tarot, and the idea of two opposite principles uniting and producing new life.
ETA: As this card seems to allude to the Voodoo creation myth, I got this from Wikipedia:
"Damballah (Sky-serpent loa and wise and loving Father archetype) created all the waters of the earth. In the form of a serpent, the movement of his 7,000 coils formed hills and valleys on earth and brought forth stars and planets in the cosmos. He forged metals from heat and sent forth lightning bolts to form the sacred rocks and stones.
When he shed his skin in the sun, releasing all the waters over the land, the sun shone in the water and created the rainbow. Damballah loved the rainbow’s beauty and made her his wife, Ayida Wedo. Ayida Wedo represents the sky powers and is symbolized by the rainbow; wife of Damballah, she shares his function as cosmic protector and giver of blessing.
The revelations of the loa (deity) descended upon the first faithful in IfÃ, a legendary city located in Nigeria. Therefore, everything in life and all spiritual strength comes from IfÃ. The homeland of all voodoo devotees, where IfÃ is located, is Ginen, from where they were forced to flee in the African Diaspora. In death, the higher soul will return to Ginen (the world of the dead, said to be under the water below the earth) to reside with the loa and the ancestral spirits. Because of this, all practitioners of voodoo refer to themselves as ti guinin, sons or daughters of Ginen."