I think tattoos, piercings and the likes are good signs of the expression of belonging to the majority. Even though a relatively recent study denies any significant correlation between general intelligence and tattoos (
http://www.sciencepublishinggroup.com/journal/paperinfo?journalid=201&doi=10.11648/j.pbs.20150404.14), we know how such quick studies can be coined up when support of certain manipulative/monetary interests dictate so.
I have theorized (and supported with some research thanks to Eysenck) that introversion is a sign of a relatively higher intelligence:
http://www.intelligentpeopleforum.com/threads/high-intelligence-and-introversion-do-they-go-hand-in-hand.5/I consider tattoos to be an indication of greater social comfort, where the individual is content with putting sexual availability on a rather clear display (
https://link.springer.com/article/10.1007/s10508-013-0104-2). Such a comfort comes naturally for the extravert, i.e. the person who feels comfortable within the majority of society, because they together occupy the center of the bell curve (they are average).
http://www.intelligentpeopleforum.com