SYMBOLS IN HINDUISM

Symbols are easy way to denote complex ideas. Hindu religion is symbolized more particularly by sign or mark of “Om”, Swastik, Tilak, etc. Sacred Hindu symbols are considered very auspicious and displayed in homes, work places, temples etc. to invoke good fortunes. 

Om (Aum, ॐ):
The significance of Om is as under:

1. This is sacred sound symbol that represents Universe; the ultimate reality (Brahman).
2. It is prefixed and sometimes suffixed to all Vedic mantras and prayers.
3. This syllable is constituted of four sounds i.e. अ (a) + ऊ (u) + म (m) + . (salient sound of dot on Aum) which represent the Creator (Brahman), the preserver (Vishnu), the annihilator or transformer (Shiva) and universal consciousness respectively.    
4. The pronunciation of Aum moves through all possible human linguistic vowel sounds and is different from the pronunciation of Om.
5. In verse 1, the Mandukya Upanishad, the syllable represent all  states of time i.e. the past, the present, the future and time  that transcends time.
6. In verse 2, the Mandukya Upanishad, the syllable represent the four states of Self i.e. seeking the physical, seeking inner thought, seeking the causes and spiritual consciousness, and the fourth state is realizing oneness with the Self, the Eternal.
7. In verses 3 to 6, the Mandukya Upanishad enumerates four states of consciousness: wakeful, dream, deep sleep and the state of ekatma (being one with self, the oneness of self). These four are A + U + M + "without an element" respectively.
8. The Shvetashvatara Upanishad suggests that Om is a tool of meditation empowering one to know the God within oneself, to realize one's Atman (Soul).
9. The Aum sound is claimed to be cosmic sound.

Swastika (स्वास्तिक ):
The significance of swastika which comes from Sanskrit (Devanagari: स्वस्तिक) is as under:

1. It denotes a "conducive to well-being or auspicious". The clockwise symbol is called swastika symbolizing surya (sun) and prosperity, while the counterclockwise symbol is called sauvastika symbolizing night or tantric aspects of Kali.
2. It represents honesty, truth, purity and stability.
3. Its four angles or points also symbolize the four directions, or Vedas.

Tilak (तिलक ):
The tilak is worn usually on the forehead on a daily basis or on religious occasions. The tilak is applied with ash (vibhuti), sandalwood paste, red kumkum etc. It has various shapes depending on deities or sects such as three horizontal lines across the forehead, a bindu, U shape etc. The significance of tilak is as under:

1. As per chapter 2 of Kalagni Rudra Upanishad, a Shaiva tradition text, explains the three lines of a Tilaka as a reminder of various triads: three sacred fires (kitchen fire, fire offering made to ancestors and fire of homa), three syllables in Om (A U M), three gunas (Sattva, Rajas & Tamas), three worlds (earth, atmosphere & heaven), three types of atman (external, inner and highest self), three powers in oneself (Kriya - action, will power & Brahman-ultimate reality), first three Vedas (Rigveda, Yajurveda & Samveda), three times of extraction of the Vedic drink Soma (morning, midday & dusk extraction of soma).
2. As per Vasudeva Upanishad, a Vaishnava tradition text, similarly explains the significance of three vertical lines in Urdhva Pundra Tilaka to be a reminder of Brahma, Vishnu, Shiva; the Vedic scriptures – Rigveda, Yajurveda and Samaveda; three worlds Bhu, Bhuva, Svar; the three syllables of Om – A, U, M; three states of consciousness – awake, dream sleep, deep sleep; three realities – Maya, Brahman and Atman; the three bodies – Sthula, Sukshma, and Karana.
3. Worshippers of the Goddess (Devi) wear a large red dot of kumkum (vermillion or red turmeric) on the forehead.

Moli / Kalawa (कलावा, :
This is sacred thread which binds one person to another symbolizing protection provided by one who binds it to another.

Kalash ( कलश ):
A vessel filled with water, five green leaves placed on it and a coconut put on the leaves. The Kalash is believed to contain amrita, the elixir of life, and thus is viewed as a symbol of abundance, wisdom, and immortality. Metal pot or Kalasha represents material things: a container of fertility - the earth and the womb, which nurtures and nourishes life. The mango leaves associated with Kama, the god of love, symbolize the pleasure aspect of fertility. The coconut, a cash crop, represents prosperity and power. The water in the pot represents the life-giving ability of Nature.

Yantra (यंत्र, ):
The Sri Yantra or Sri Chakra consists of nine interlocking triangles that radiate from a central point. Of the nine, the four upright triangles represent the masculine side or Shiva; while the five inverted triangles represent the feminine, or the Shakti (Divine Mother). As a whole, the Sri Yantra is used to symbolize the bond or unity of both the masculine and the feminine divinity. It can also mean the unity and bond of everything in the cosmos.
  
Shankh (Counchshell, ):
Shakh or sea shell is used as trumpet in Hindu rituals. Shankh is believed to be a giver of fame, longevity and prosperity, the cleanser of sin and the abode of Lakshmi, who is the goddess of wealth and consort of Vishnu.
Diya or lighting lamp (दिया :
This symbolizes one of the five panchbhoth (earth, fire, water, space and air) and treated as sacred.
 
Shri or Shree (श्री):
Shri refer to goddess Lakshmi.
 
Saffron Flag:
Dhvaja, or 'flag,' is a symbol of victory, signal to all that "Sanatana Dharma shall prevail." Its color betokens the sun's life-giving glow.
 
Hands in prayer:
It is a sign of respect for the sacred, that which is dear to the heart.
 
Lotus (padma):
It is a symbol of purity/transcendence. Growing out of the mud, it is beautiful, and though resting on water, it does not touch it.
 
Trident (trishul):
It is the symbol of Shiva carried by shaivites.
 
Cow:
It is a symbol of purity, motherhood and ahimsa (non-violence).
  
Lotus feet (of guru or deity):
It is touching the feet of superiors’ shows an attitude of submission and service.
 
Reference:

1. https://en.wikipedia.org/wiki/Hindu_iconography
2. https://en.wikipedia.org/wiki/
3. http://www.ancient-symbols.com/hindu-symbols.html