The practice of tattoos and tattooing means different things in different cultures. In early years the most common reason for getting tattooed seems be Decoration, which is still the most common reason today.
In some cultures tattoos where used as an Identification of the wearer's status in a group. This is still done today by most tribes in Africa, Australia and the South Seas. In certain cultures you can't get a tattoo just because you want one. You will have to earn it. Boys reaching manhood receive one to mark this special occasion, different styles are applied when men get married and so on. Mokos, Polynesian and Maori facial tattoos, are just applied on Warriors after they did something brave and heroic for the tribe.
The ancient romans for example used to tattoo their slaves and criminals to recognize them easier and it was the same with most of the Jews in WWII. Tahitian tattoos were used to tell the story of the wearer's life and served as Rites Of Passage.
The tattoo culture we have now in the western hemisphere began with sailors traveling to exotic foreign lands collecting tattoos in every harbor they were stationed. The different motives they were carrying showed the different places they were stationed. A dragon, for instance, meant the wearer served on a station in China or Japan. Tattoo parlors started to shoot out of the ground in every port city around the globe.
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