When I was a kid, I read an article in school that had a similar theme. They paint the grill marks on burgers, then I think they used salt to draw the moisture out and make them look juicy.
I worked at Harvey's (Canadian burger chain) while I was in school and they were obsessed with grill marks. It got to the point where you would cook the burg mostly on one side to get that nice dark cross hatch, and then cook the bottom just enough so that it was cooked through. The customer would only see the top, and it was important that it resembled the advertising.
Grill marks on a medium rare steak are proof that whoever cooked it knows what they are doing, burgs not so much.