There are various ways in which these two interrelated concepts can be looked at. Like the tre-gun they compose a vital part of the Nihang Singh philosophy. In the Chandi Chariter, Sri Guru Gobind Singh Ji writes; 

'The Lord is Primal, Infinite, Account-less, Boundless, Deathless, Garbless, Incomprehensible and Eternal. He created Shiva-Shakti, four Vedas and three modes of maya and Pervades in three worlds. He created day and night, the lamps of sun and moon and the whole world with five elements. He extended enmity and fight between the gods and demons and Himself seated (on His Throne) scans it.1'. (Dasam Sri Guru Granth Sahib Ji, 175)

The Sikh writings suggest a great significance of the union between Shiv and Shakti;

When the play of Shiv and Shakti comes to mind, one remains dead while yet alive'
(Sri Guru Arjun Dev Ji, Adi Sri Guru Granth Sahib Ji, 1257)

'Wherever I look I see the Lord pervading there in the union of Shiv and Shakti.'
(Sri Guru Nanak Dev Ji, Adi Sri Guru Granth Sahib Ji, 21)

'When Shiv and Shakti playfully united the whole world came to be.'
(Bhai Gurdas Ji, Vaar 2, Pauri 19).

There are various ways in which Indian philosophies understand the notion of Shiv-Shakti. Shiv may be seen as Shiva and Shakti may be seen as his consort or more generally a feminine counterpart of a deity. Thus, we have a concept of divine masculine and feminine energy. Within the Indian traditions Shiva without Shakti is referred to as Shava, meaning corpse. This can be compared to a human being whose conscious is not aware of Vaheguru; Shiv may also be interpreted as consciousness and Shakti as divine power, hence a conciliation of the two represents conscious absorption into the Divine. Shiv may also refer to the soul (which is the very form of Vaheguru) and Shakti the power of Vaheguru transcended from nargun (formless) to sargun (with form - i.e. the universe). The great treasure of knowledge, Sant Giani Gurbachan Singh Bhindranvale (1902-1961) discusses that within certain context Shiv can also mean Satogun and shakti can represent Tamogun.(Adi Sri Guru Granth Sahib Katha, Volume 12, .020). He also states that Shiv can be understood independent of the deity Shiva, and as the form of Parmeshvar (Primal Being) and that Shakti can be understood as maya (creation).

Mahant Om Nath Sharma in an article titled 'Navarati' gives the take on Shiva and Shakti from his school of thought that translates Shakti as Durga (the divine mother of the universe):

Durga represents the divine mother. She is the energy aspect of the Lord. Without Durga, Shiva has no expression and without Shiva, Durga has no existence. Shiva is the soul of Durga; Durga is identical with Shiva…Shakti is the omnipotent power of the Lord, or the Cosmic Energy.
(A Mystic World, Vol 1, Issue 1, page 18)

There are a wide range of complementary understandings all which allow one to analyse the interaction of Shiv-Shakti within the Nihang Singh at various levels.  Shiv is believed to be represented by a half moon (Aad Chand), signifying calm and coolness. Shakti is represented by a sun and is believed to be a more powerful energy and the driving force of the universe, within the Sikh tradition Chandi (personification of shakti) or Durga is not worshipped as a deity, but in the form of Bhaguati (sword). The Aad Chand (crescent moon) representing Shiv has long been a trademark of Nihang Singhs as is the wearing of arms; representing the divine union of Shiv and Shakti.

Nihang Baba Hari Singh Ji - Baba Bakala Dal

The highly treasured Nihang Baba Hari Singh Ji of Baba Bakala Dal seen (above) adoring the Aad Chand in his dumalla (Nihang turban style ) surrounded by various small Bhagautis representing the game of Shiv and Shakti.

Shiv Shakti is not limited to mere symbology and external guise, it extends to spiritual practice. In line with the earlier explanation by Sant Giani Gurbachan Singh Bhindranvale, Shiv may also mean those who are inclined towards the Lord. Those inclined to this path follow the practice of Bhakti, devotional worship. Therefore, we also find that the relationship between Shiv-Shakti at times referred to as Bhakti and Shakti. Baba Tirath Singh Nirmala in his translation of Pundit Gulab Singhs Bhavrasamrit (p42-44) mentions the nine limbs of Bhakti which are referred to in the Sikh tradition as the Nvai Parkar (Nine methods):

1.        Sravan - hearing the divine* praises.
2.        Kirtan - singing the praised of the divine.
3.        Simran - remembrance of the divines name.
4.        Padsevena - service and offerings at the divines feet.
5.        Archana - worship the divine.
6.        Bandana - prostration before the divine.
7.        Dasyam - developing feeling or emotion of being the divine's servant.
8.        Sakhyam - cultivating the emotional bond of friendship.
9.        Atma Nivedana - surrender of the self to the divine.

*Within the Sikh tradition it is the Divine or the Guru who is the centre of Bhakti, within Indian traditions it is often a deity around which one centres their spiritual practice.

By looking at the traditional practices of the Akali Nihangs, it will become clear how much of an important role is played by Bhakti. An example can be seen in case of Jathedar Baba Teja Singh 96 Krori who lead the Nihang Singhs of Budha Dal from 1907-1929. Unable to afford traditional instruments for the performance of kirtan, Baba Teja Singh upheld this import tradition by using his karray (iron bangles) as musical instruments. For many years he performed kirtan by banging his karray.

The nine limbs of bhakti form an everyday part of a Nihang Singhs life. Everyday involves hearing and singing the praises of the Divine, they are taught to engage in the remembrance of the Divine 24 hours a day. The Aarti prayer is read everyday in worship of the divine. Many Nihang Singhs dedicate to their life serving at one particular Gurdwara. Being the ladlian faujan, beloved army, of Sri Guru Gobind Singh Ji who they believe to be their eternal master portrays the deep bond they experience with their Guru. Many people overlook or actively undermine the Nihang Singhs without failing to realise the deeper esoteric value and spiritual philosophy behind their every action. Their lifestyle is their bhakti, Shakti they gain through their dedication to Bhagauti and Sabrloh (pure iron).

Jathedar Baba Chet Singh Ji 96 Krori, the 12th Jathedar of the Budha Dal

Well respected figure of the past century, Jathedar Baba Chet Singh Ji 96 Krori, the 12th Jathedar of the Budha Dal. Large sarbloh prayer beads (representing bhakti) can be seen around his neck and in his hand. He can also be seen adorning various weapons (representing shakti) by his side and in his dumalla. From the entire apparel of the Nihang Singhs one can witness the union of Shiv
and Shakti which is Divine.

The late Jathedar Baba Santa Singh 96 Krori of Budha dal discusses the meaning of 'shakti' which he believes is something many Sikhs fail to understand;

"We call that Shakti what Sri Guru Nanak Dev Ji has written is the mother of the universe and who has created Brahma, Vishnu and Shiva (quotes 30th verse of Japji Sahib). God being confined within himself gave hukam (command) for his power to become manifest, that Shakti created the whole world and thus takes the form of the mother….some worship Shakti as Bhavani, others as Kalika  and others as Chandi. We worship this shakti in the form of our weapons." (Audio Recording, April 1995)

Despite the great significance of Shiv-Shakti, Bhagat Namdev teaches it is useless to indulge in deep consideration on such philosophical matters if one does not meditate on the Master of the universe, which is the greatest of all acts. (Adi Sri Guru Granth Sahib Ji, 873). Such matters exist within our temporal realm and an understanding of them helps an individual on their spiritual path. When one reaches ultimate stages of divine bliss such matters cease to be important. The fifth Guru, Sri Guru Arjun Dev Ji describes this state;

'There is no Shiva or Shakti, no water or wind, no world of form where the True Guru, the Yogi,
dwells, where the Imperishable Lord Vaheguru, the Unapproachable Master abides.'
(Adi Sri Guru Granth Sahib Ji, 883)

The Khalsa internally and externally illustrates the great divine play between these forces. These concepts should be used to aid ones understanding of creation and not hinder their relationship with the One Supreme Being. Sri Guru Arjun Dev Ji reminds us that millions Shiv and Shakti are under the command of Vaheguru (Adi Sri Guru Granth Sahib Ji, 1156).