Tattoo culture in the United States is quite interesting.
For example, spider webs are a type of prison tattoo, signifying that the person has served a long sentence. Teardrops can mean the person has killed someone or is mourning a close friend or relative who has passed away.
Beyond that, tattoos are also a part of regional gang culture. They give gang members a sense of heritage and identity, while also serving to flaunt their status and intimidate rivals, creating a hierarchy.
When Harry mentioned that the tattoo in the photo belonged to a member of the Turing gang from Las Vegas, Dean finally remembered.
He had indeed seen that tattoo in Las Vegas!
Remember Santoni? He was a former medical examiner from the Los Angeles Forensics Department. After creating a fake autopsy report for Dean's father, he resigned and disappeared without a trace. Mas later discovered his whereabouts.
Mas also died unexpectedly when he went to meet Santoni.