Anybody knows what Mani's tattoos represent??

Not sure. It depends on if the tribe is entirely fictional or based on a real tribe.
But seeing as we never heard a name of the tribe (or ranks or such), I think it's all just fictional.

His tattoos could potentially also not mean anything, considering that a tribe could have 'basic adulthood' tattoos alongside tattoos that do have a meaning and need to be earned in specific ways.

I feel educated, thank you