The majority of policemen I know have tattoo's. They aren't frowned upon and they also hold a very high status amongst civilians.
Don't be so old fashioned. Tattoos are acceptable in many professional careers, and if it's hidden, then how is a passenger going to see anyway? Nobody needs to know. As rockrats said, he doesn't go shoving his arm in front of every second person saying "look at this", it's personal, no need for a show to anyone, no passengers would ever know.
However, if rockrats happened to be a 'tattoo wearing yob', then maybe that would be the case for calling his tattoos disgraceful. However, they appear not to be.