1. Om (ॐ): This is perhaps the most well-known Sanskrit symbol and is often associated with the union of the universe, the individual self, and the divine. It is seen as the sound of creation and the ultimate reality.
2. Yantra: These are geometric diagrams used in Hinduism and Buddhism. Certain yantras, such as the Sri Yantra, are believed to represent the union of different energies and forces, ultimately leading to enlightenment.
3. The symbol of Shiva and Shakti: Shiva, the male deity, and Shakti, the female deity, are often depicted together as a representation of the union of the masculine and feminine principles, the two essential forces of creation.
4. The symbol of Ardha-Nareeshvara: This is an iconographic representation of Shiva and Shakti united as a single being, with half of their bodies merged. It symbolizes the union of opposites and the interconnectedness of all things.
5. "Samyoga" (संयोग): This Sanskrit word itself means "union" or "joining together" and can be used as a symbolic representation of the concept.
Ultimately, the best symbol for "union" will depend on the specific context and the desired meaning. It's important to consider the different symbols and their potential interpretations when choosing one to represent union.