I have been staring at these four characters for a while now. I don't know what the person wanted the tattoo to represent. The only way to interpret it is to go character by character:
子 = child, son, seed, offspring, egg, pellet, or bullet (depends on context).
手 = hand.
術 = proceed, method, or technique.
流 = flow, smooth, fluent, or drift (depends on context).
The closest definition I can come up with is: "smooth technique of hand to achieve seeds". It sounds like this dude enjoy "polish his own knob" a lot.
Regardless, the direction of the characters is reversed.