Laws of all kinds differ from country to country worldwide, and the same goes for rules around tattoos. Each service can set their standards. The safe way to go is nothing racist/extremist/obscene and nothing visible in Class A/dress uniform. So nothing above the collar or below the wrists.
Many Muslim countries have laws banning tattoos that involve any quotes or imagery related to religion. The content of all tattoos in these nations is subject to Sharia Law. These countries include Malaysia, Saudi Arabia, Yemen, Afghanistan, and Pakistan. So, tattoos aren't illegal in these countries, but they must be respectful to the local culture and religion.
Tattoos are not allowed on the sleeves, legs, and arms of the soldiers. The tattoo must not be visible on any part of the body of the soldier that is exposed while wearing any of the military uniforms. The army bans having a tattoo on the head, neck, and face. Tattoos below the wrist bone are allowed.
No having a tattoo does not forbid you from joining any Armed forces in Pakistan But there are certain regulations about it, the tattoo should only be on the inside of your forearm and nowhere else.
If you have a traditional tattoo or something very sentimental in terms of your sector tribal group you need an authoritative document that tells people that you are belonging to that particular group and the atop is recognized to the group you belong to.
However, tattoos, which are offensive to modesty, decency, or propriety and those that advocate a philosophy that demeans a person based on gender would not be permissible for all. Similarly, racist tattoos that advocate a philosophy that degrades or demeans a person based on race, ethnicity, or region and religion would be prohibited for all categories.