It should be fairly obvious from the article (and image) it refers to tattoos that are in direct contact w/ the watch.
Also, it's funny and sad watching the amount of conservative folks pretending this isn't a defect by instead bashing people with ink. I guess if you live on a farm in Kansas tattoos seem like this 'zany' thing, but in cities they're pretty much the norm. I'm almost in shock when I come across someone who doesn't have a tattoo these days. Either way, tattoo or not, it's sad to see so many Apple fans displaying vitriolic comments about other people's decision to get a tattoo. That kind of nastiness looks far worse on you than a tattoo ever would.
It is not a defect.