I am practicing as an LAPC at the moment. I have 3 tattoos, two of them are on the inside of my bicep of each arm, fairly large. I work with kids, and I often wear short sleeve shirts or polos and sometimes my tattoos become exposed. The kids don't mind. I once had a parent state to me that they were offensive to her because from where she came from she interpreted tattoos as a gang symbol. Mine are religious in nature, I explained it, but she still didn't like it, and they terminated therapy early. It can go either way.
Also, as another poster put it, it is a form of self disclosure. There have been a few times where my tattoos peeked out and I had to explain their non-Christian significance to strongly Christian clients earlier than I would have preferred in the course of the therapeutic relationship.