I'll say I can see how the ideas/themes with shock-value or darker/sinister tones hold a certain amount of allure. I believe it's because we all have to hold our tongues and not react, in our everyday life, towards people who really friggin deserve that we react to them! And we have to put on the good-boy or good-girl act in terms of the face we show the world.(never understood the fascination with skulls and other sinister looking stuff)
Rant over.
Therefore I view that darker themed tattoo as like a warning sign telling whomever the other person is that is gazing upon it that if they had thoughts of trying to be sly and do something shady with you... that they'd better reconsider that thought.
It also shows me that this person is un-encumbered with fearing about falling-in-line with what society views as a norm. Even if I don't dig on whatever art-work that other person got put onto themselves... you can at least respect that they committed to doing it, a thing you can't turn back from. And were willing to pay for it and endure the discomfort.