The tattoos are placed so that when wearing a jacket, they can't be seen, but are revealed when the jacket is removed. To elaborate on what jjgifford said, when a new member of the Yakuza is initiated, they are forced to amputate the end of their pinky finger. If they screw up, they have to cut off the rest of the finger. Also known as The Poison Fist of the Pacific Rim.

"They'll kill ya five times before ya hit the ground!"
- Agnes Skinner