Potterhead Jonathan Trenberth from Married at First Sight NZ was put to the ultimate Harry Potter Trivia by JBS today and one of the trivia questions was regarding Dumbledore's scar on his left knee.
Jonathan did not know what it was but apparently, according to Jono's google search, Dumbledore's scar was:
a map of the London Underground...
Here's an excerpt from Chapter 1 - The Boy Who Lived for you Potterheads out there fact checking Jono's google search:
Scars can come in handy. I have one myself above my left knee that is a perfect map of the London Underground.