It maybe mentioned, but I skeemed through and didn't see it. You can get grill marks on anything, but you have to have the temp turned up. I have a gasser and let my grill warm up on hit, so the racks get real good and hot, and then I turn it down to my cooking temp for the cook. The hot racks will give you the marks your looking for.
NOW, if you want perfect 90 degree marks ... place your meat (not THAT meat) between 10/11 and 4/5 ... cook for however long and then rotate to between 1/2 and 7/8
Using that will give you grill marks like this