Permanent tattoos in general because one is unnecessarily making a permanent change to their body for the purpose of beautification. And in general, that's forbidden. More info: http://www.islamqa.com/en/ref/20283
I suppose that's why they don't shave either?
> one is unnecessarily making a permanent change to their body for the purpose of beautification
What kind of shaving do you do?
A man shaves every day he will go his entire life without a beard, is that not permanent?
In any case you can't shave on the last day of your life.