i personally think its a bad idea, or useless. its much better to visualize the hung in your mind than to actually tattoo it on your body. it just becomes a burden to carry and a cause of dissatisfaction and resentment in the long run. i can talk from some experience since i have a tattoo on my leg. i experienced those negative emotions and stuff for getting the tattoo but now im just indifferent and dont care about it anymore, its there. it didnt change anything about me or was not of any benefit whatsoever. and i think the buddhist teachings advice to let go of grasping and clinging and attaching some picture or symbol into your body goes against that teaching or advice from my perspective. from experience i can say that you will just get some more load to carry around with you. its a burden.
If the thought of demons
Never rises in your mind,
You need not fear the demon hosts around you.
It is most important to tame your mind within....
In so far as the Ultimate, or the true nature of being is concerned,
there are neither buddhas or demons.
He who frees himself from fear and hope, evil and virtue,
will realize the insubstantial and groundless nature of confusion.
Samsara will then appear as the mahamudra itself….