One of the more popular tattoo designs would include skulls.
Skulls can serve a number of symbolic purposes. The most common being of death and mortality. But, one can use the image of a skull to symbolize various things.
Other Skull symbolism include:
Overcoming a tough time
A past life, now changed, never to revert.
Although, at first glance they may appear to resemble a gothic, negative, or some such image, they do not always mean what they resemble. The meaning behind a word, is just as strong as a meaning behind an image.
Skulls can be drawn as cutsey doodles, demonic spirits, celebrations, etc.
Each person that chooses to have a skull tattooed on his/her body, has a reason and a means. Not every case is a skull meaningful, but in many, they can be.