I didn't know that having a tatoo, visible or not would affect how one performed as an airline pilot!
However, I must agree that visible tatoos do look un-professional.
I have a small tatoo on my right upper shoulder of "downwind". Its less than an inch across and it can't be seen through a white shirt. I doubt it will cause problems. In fact in a recent medical the examiner thought it was done very tastefully and looks professional.
Savage