In terms of sociology, the most interesting things about tattoos would have to do with which groups of people do or do not have tattoos.
I would do research into the topic to confirm that there have been changes in the groups of people who have tattoos. I believe that tattoos began as very much a lower class thing. In past times, a "normal" middle class person would never have a tattoo. This would have been especially true of women. Now, tattoos seem to be quite prevalent among all classes of people.
I would try to make a sociological argument as to why tattoos have become more popular and why they have lost the stigma that they had as recently as 2 or 3 decades ago.
To many, a tattoo is thought of as being a permanent decoration, a good cosmetic change. Furthermore, tattoos are popular among teenagers and young adults. In fact, tattoo art or tattoo quotes may be used as a permanent memorial for something close to you.