The Moon and the Serpent
The location of the Moon on the left side has another significance. It is indicative of the iḍā-nāḍī ("Iḍā-Channel"), also called Candra-nāḍī, and refers to the Pitṛyāna ("The Path of the Forefathers"). Further, the Moon is also sometimes a taken as a symbol of jīva, the individual self, as both are represented as having 16 digits, as in Chāndogyopaniṣad 6.7.1 ṣoḍaśakalo vai puruṣaḥ. And as the Jīva Principle is itself sacred, Śiva bears it, under the guise of the Moon, on His head. The jīva in its pure state neither waxes nor wanes, and it is only in the impure state that it goes through fluctuations.
The next item to be observed is the serpent on the crest. The iconography of the serpent with its open hood, on or behind the head of a devatā is a common element in iconography. The reference is obviously to the Kuṇḍalinī serpent in its aroused and arisen state, confirmed also by the proximity of the Moon. For we read in the Śāradātilaka 25.64 :
mūlonnidra-bhujaṅga-rāja-mahiṣīṁ yāntīṁ suṣumnā''ntaram
bhittvā''dhāra-samūham āśu-vilasat-saudāmanī-saṁnibhām |
vyomāmbhoja-gatendu-maṇḍala-galad-divyā'mṛtaugha-plutāṁ
sambhāvya svagṛhaṁ gatāṁ punar imāṁ sañcintayet kuṇḍalīm ||
मूलोन्निद्र-भुजङ्ग-राज-महिषीं यान्तीं सुषुम्नाऽऽन्तरम्
भित्त्वाऽऽधार-समूहम् आशु-विलसत्-सौदामनी-संनिभाम् ।
व्योमाऽम्भोज-गतेन्दु-मण्डल-गलद्-दिव्याऽमृतौघ-प्लुतां
सम्भाव्य स्वगृहं गतां पुनर् इमां सञ्चिन्तयेत् कुण्डलीम् ॥
[Abdicating the state of sleep, and rising from the Mūlādhāra-cakra, the Serpent Queen penetrates the Suṣumnā. Piercing through, She blazes like lightning. Getting aspersed in the divine nectar oozing from the orb of the Moon situate in the Lotus Celestial, She finally returns to her abode. The aspirant must contemplate on Her.]