This used to be a good rule of thumb to avoid bad people but unfortunately (because I hate tattoos) it's been mainstreamed and more and more normal people are getting them done. It could be less that they are a troubled mind or impulsive and more that they are someone who follows trends and just likes the style. It's easier for a responsible person to get away with a discreet tattoo than it was in the past. Even in Japan some hot springs are loosening the rules against visible tattoos because too many young people are inked these days.