Working as an emt, our companies' policy is that tattoos can be showing as long as they aren't "excessive or offensive." I had worked with the tattoo on my right arm for 3 years with prior permission, and then we got a new supervisor whose interpretation of that ambiguous rule meant that I had to get long sleeves. Of course, as I get more work done and the ozone isn't what it used to be, I am more than happy to cover them up. Twelve hour work days with one of your arms getting blasted through the window= a kickass farmer's tan and a faded tattoo.
As far as previous discrimination goes, I've only had a couple of patients who had issues. Both of which were elderly, and I just told them my kid got crazy with a permanent marker.
With most it is just a conversation piece, which has been helpful is distracting them from whatever issue they may be having at the time. We had this quadriplegic fellow with chronic px going to a routine appointment. That guy had a lot of work done and we sat for 45 minutes bullshitting about tattoos and 80's/90's metal while waiting for the dr.