Boys have tattoos. Men have scars.
haha like this one. 
I had a job servicing communications systems and I was at a Hospital doing fault finding.
I walked down a hallway that was also a photo display gallery...
There was a photo from the early 1930's taken of a surgical team in the operating room just after they closed up the patient and wheeled him out, but before they cleaned up...
The Surgeon had a Heidelberg dueling scar.