Some people use tattoos to mark accomplishments or the passage into a new life stage. Challenges faced, people killed etc.
Some people use the tattoo to show that they are part of the culture of the people around them; to put their cultural identification on their skin for all to see.
Some people use tattoos to indicate they are not part of the larger dominant culture and appear to rebel against the dominant culture or their parents. People want to be special.
That tramp stamp does send a clear message. Thanks for making things memorable.