While over Greenland, the jet says, "Hey we're getting pretty far North...Grid Nav is ready if you need it." That's what the box enclosing "Gird 106" means; an artificial heading reference that doesn't rely on magnetic North. It's what you see when you get far enough north that conventional heading reference systems start to get inaccurate. Above 78 degrees north, compass headings start to not make sense so an artificial reference called "grid" kicks in--automatically in this airplane...which is good.