Indeed, the look is becoming so popular that there are even tights available to buy with tattoo designs printed on them! The trend was started by British model Lily Cole in one of her adverts, and has snowballed ever since. A large number of tights manufacturers are printing ever-more intricate designs onto their sheer hosiery to give people ready-made 999 tattoos without the pain of the real thing, with a wide variety of styles and designs to choose from. Some people are even choosing to create their own DIY versions, so they can have the exact design that they're looking for.
The question of whether tattoos showing through tights are a problem or a fashion statement largely comes down to the setting that you're in. If you're in a professional workplace it's most definitely a problem, as you're highly unlikely to be taken seriously and it can look extremely unprofessional. However, in a more relaxed atmosphere it can certainly be a fashion statement. But, if you're happy to show your tattoos off and the situation allows it, why cover them up at all?