From The Pew Research Center:
March 24, 2010
Tattoo Taboo?
72% The great majority of adults with tattoos (72%) say they are usually hidden from view.

Most adults with tattoos, whether young or old, don’t display them for all the world to see. When asked if their tattoos are usually visible, the vast majority (72%) say that they are not. This is true for Millennials and their older counterparts.

Among those with at least one tattoo, 70% of Millennials and 73% of those ages 30 and older say their tattoos are not usually visible. Men are more likely than women to have tattoos that can be seen by all — 23% vs. 13%.

This pattern is consistent across age groups. When asked whether their tattoos are usually visible, roughly one-in-ten tattooed women volunteered that it depends on what they are wearing.
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Among Youth:

Nearly four-in-ten have a tattoo (and for most who do, one is not enough: about half of those with tattoos have two to five and 18% have six or more).

Nearly one-in-four have a piercing in some place other than an earlobe — about six times the share of older adults who’ve done this. But their look-at-me tendencies are not without limits.

Most Millennials have placed privacy boundaries on their social media profiles. And 70% say their tattoos are hidden beneath clothing.

See the full report,  Ch 4 & 7)