Shankha + Chakra — Lord Vishnu's two main weapons.                      

Meaning:1. Shankha (Conch):The sound of creation - OM. In Yoga, it means Pranayama, breath, life energy (Prana)When you blow Shankha, it clears negative energy and purifies the mind. That's what yoga does.

2. Chakra (Wheel):Called Sudarshana Chakra — means "good vision"In Yoga, it is Dharma Chakra / Wheel of Life — Karma, cycle, balance, timeIt also represents the 7 Chakras in our body — Muladhara to Sahasrara.

Together — Shankha on Chakra means:
Sound + Movement, Breath + Balance, Spiritual Power + Protection