Adopting a slogan/anthem that can be acclaimed to distinguish a certain group of people from others, or a certain state from others is one of the permissible matters. The Muslims in the past had a slogan which they used when they met their enemies on the battle field.
This was used at the time of the Messenger of Allah صلى الله عليه وسلم and by his agreement. They took the slogan of (Ha Mim, they are not helped) in the battle of the trench and Qurayzah, and the slogan of (You, the helped, bring death, bring death) in Banu Al-Mustaliq, and so on.
This is besides the favours bestowed by Allah سبحانه وتعالى upon man of the characteristics created in him such as hearing, sight and speaking, all of these are included in the evidences of ibaha. So, man sees, speaks and applauds whatever he wants unless there is specific evidence related to any of them, which then he must observe.
Therefore, it is allowed for the Islamic State to adopt a slogan with which it applauds and by which it distinguishes itself from other states, where it uses it in its relations with other states, and it accompanies the Khalifah in his visits to other heads of states or during their visits to him. It can also be used by the public in their occasions, where they applaud with it in their assemblies, public gatherings, schools and broadcasts, and the like.
In regards to the method of applauding, i.e. the intensity of the voice, the lowering, or speaking with or without a nasal sound etc, all of this is allowed, because the Muslims used to declaim their poems with an exciting voice in accordance with the occasion they were applauding.
The state has adopted that it should have an anthem, which it uses when necessary, and it accompanies the Khalifah in his official meetings with the heads of states. Additionally the Ummah would use it on certain occasions.
The following has been noted for the anthem of the second rightly guided Khilafah after its establishment by the permission of Allah سبحانه وتعالى:
1 - It should mention the fulfilment of the glad tidings of the Messenger of Allah صلى الله عليه وسلم regarding the return of the second guided Khilafah, and the rise again of the banner of the Uqab, the banner of the Messenger of Allah صلى الله عليه وسلم.
2 - It should mention the glad tidings of the Messenger of Allah صلى الله عليه وسلم when the Khilafah is established and the earth will bring out its treasures and the heaven will send down its blessings, and the earth will be filled with justice after being filled with tyranny.
3 - It should mention the conquests and spreading of goodness in all of the worlds regions with the Khilafah ruling over all, particularly the lands of the three mosques to which journeys are made: al-Masjid ul Haram, the prophetic masjid, and al-Masjid ul-Aqsa after uprooting the Jewish entity.
4 - It would be concluded by the return of the Ummah as Allah wanted her to be: The best Ummah brought to mankind, where its main goal is to attain the good pleasure of Allah سبحانه وتعالى, Who would honour her with His favour, Mercy and the High Garden of Al-Firdaws.
5 - Takbeer has to be repeated in it. This is because takbeer has a special impact in Islam and in a Muslim's life. It is takbeer that reiterates in their victories, and in their holidays, and on their tongues and is mentioned on every effective occasion.
The above is an excerpt from the book "Institutions of the Khilafah State" by Hizb ut-Tahrir.