Na tasya pratima asti
(There is no image of Him)
Shiva is formless. He is in everything, and everything is Him. He is happy irrespective of the form we assign to Him, but there is no single form that defines Shiva.
However, since the beginning of the Vedic period, many different symbols have been associated with Shiva so that whenever you see them, you are immediately reminded of our Supreme Lord. Here is a look at all the symbols that are attached to Him-