Shiva is termed as a state of meditation (or Samadhi as said in religious scriptures) in which there is only one thing; i.e. the world of consciousness.
This state is not easy to attain and is generally known as a state where the soul is very alert & attentive but no action is taken.
Hence, the snake in the neck of Lord Shiva represents that alertness.
When you meditate, your eyes are closed, but it does not mean that you are sleeping. The serpent in the neck of Shiva signifies the alertness of your soul.
The Trishul (trident)
The trident that Lord Shiva is seen holding in most of its representations is also called as Trishul.
Shul means problems or suffering; hence Trishul means something that eradicates all your problems.
The Trishul also represents the three state or factors of consciousness such as waking, dreaming, and sleeping.
The depiction of Shiva holding the Trishul means the great yogi is above all the three states. Despite this, Shiva holds these states together.
Click next slide for more forms of Lord Shiva