We think that God Shiva has got the 'damaruka' or drum in one hand or trishula on the other hand and we visualise His form that way.
Similarly,in one hand of Vishnu,there is a chakra and in the other hand,there is a sankha or conch.Sankha represents sound.Chakra represents time.Vishnu has taken the symbols of sound and time in both His hands.In case of Shiva,the drum represents the sound and Trishula is trikala,the symbol of the past,present and future.
Similarly,what Vishnu has in his hand is sound and time.In the same way,what Shiva has in his hand is also sound and time.The differrence is in the form and the name only,but the energy or power is the same.
(SSB.1972 p .175 )
From 'Do you know, ( sai baba )