I work at an AFB and our dress code says nothing about body piercings or tattoos. It talks about wearing stuff like "tank tops, midriff tops and shorts" but I know that alot of women wear sleeveless shells to work and they aren't talked to so those aren't considered "tank tops".
I don't think they would want to address the issue of tattoos because it would affect so many of the shop guys and women and the heat here in the summer is between 90-100 there is no way that the Union would stand by and allow that to go through. They would argue that it would be putting people's health at risk for something so stupid as covering up a tattoo on their arm while they work potentially outside (if they work in Civil Engineering) when many of the military customers come walking in covered in tattoos while in civilian clothes. It would be a tough fight for management to win, I think.
I personally have a pink ribbon tattooed on my left wrist for my fight against breast cancer (in remission since Feb 2010), a small celtic dragon on my right wrist and several tattoos on both legs (visible when I wear a skirt) and a small diamond piercing in my nose...no one in management has EVER said anything and I am a Program Manager with almost 17 years here at the same job!