What is the significance of different types of flag posts on the top of temples?

Question

On the top of temples we often see different kinds of flag posts. On temples of Vishnu we see a chakra, on the temples of Shiva we see a trident, and also some other types of flag posts. For example, see the below pics:

What is the reason behind it as per the scriptures? A person said that those are generally used for identifying the temple just by seeing it from the outside. Is that true as per the scriptures, are there any scriptural reasons for using the various types of flag posts on different temples?

Answer 1

So it turns out that, protection of the temple (possibly from pishacha and demonic forces) is the reason they are used on the temples. The chakra and trident are the weapons of Vishnu and Shiva respectively. Hence, chakra is used on Vishnu temples and trishula or the trident is used on Shiva temples:

vaiṣṇavādau ca cakrāḍhayaḥ kumbhaḥ syānmurtimānataḥ
sa ca triśūlayuktastu agraculāmigho mataḥ [Agni. Pu. - 102.3]

Meaning On temples of Vishnu, the chakra should be placed upon the pitcher which should be according to the size of the idol. If the pitcher is endowed with a trishula, then it is known as agrachuda.

They are empowered with mantras along with the flag and the flag staff upon the completion of their establishment on the temple top and the guru prays the presiding deity of the weapon for protection:

guruḥ pāśupataṃ dhyāyan sthiramantrādhipairyutam
ādhipān śastrayuktakāṃśca rakṣaṇāya nibodhayet [Agni. Pu. - 102.28]

Meaning
The guru after meditating on pashupata and being endowed with the presiding deities of the mantra, requests the presiding deity of the weapon for protection.

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The above reason seems correct to me, but if there are other reasons please feel free to comment, answer or edit this post and I will unaccept this answer. Thanks.

Answer 2

Two of your pictures are of the Nila Chakra on top of the Puri Jagannath temple, and there's apparently a special story for why that Chakra is on the top of the temple rather than inside; it was a punishment for the Sudarshana Chakra's pride, as described in this book:

in the age of Kali Lord Vishnu took the form of Lord Jagannath devoid of limbs and was seated like a small pole like structure. Lord Sudarshan became elated and proud for his power in the age of Kali. Lord Vishnu could know the pride of Lord Sudarshan and sent him to call Hanuman... Hanuman started for the meeting with Lord Jagannath at Srimandir... There was some altercation between Lord Sudarshan and Hanuman.... Lord Sudarshan out-paced Hanuman and to bar the entry of Hanuman to Srimandir moved with tremendous speed and guarded the four entrances of Srimandir.... Hanuman then prayed the Lord and energized himself with tremendous power, became eight-handed and held the great King of Chakras at the four entrances of Sri Mandir in fingertips of the four created hands. He then folded two of his hands as a token of respect to Lord Jagannath ... and then proceeded to have the darshan of Lord Jagannath.

Realizing the futility of the pride in the presence of Hanuman, the great devotee, Lord Sudarshan came to the Lord. As a punishment for the pride Lord Sudarshan was cursed to hide all the power and sit as a pole-like structure in the left side of Lord Jagannath. Lord Sudarshan prayed Lord Jagnnath who was gracious With his weapon the king of the chakras. He told Lord Sudarshan in the age of Kali, the king of wheels will adorn the spire of Sri Mandir as Nila Chakra. A darshan if Nila Chakra will be equivalent to the darshan at the Lord's.

Now if other Vishnu temples in North India put up a Chakra like this, I can only assume that it's in imitation of the Puri Jagannath temple, similar to how Vishnu temples often copy a lot of the features and practices of the world-renowned Tirumala Venkateshwara Temple in Tirupati.

And I assume that the practice of putting Trishulas on the top of Shiva temple has an entirely different origin.