Place each steak on a baking sheet. Combine brown sugar, salt, cumin, paprika, chili powder and coriander in a small bowl. Sprinkle half of spice rub over steaks and rub it all over top and sides of meat. Flip steaks over, sprinkle on remaining mix and rub all over that side. Cover baking sheets with plastic wrap and refrigerate for up to 6 hours before cooking.
Preheat a gas grill to high for 20 minutes. Place steaks on grill and lower heat to medium. Grill steaks for 4 to 6 minutes, flip, and continue to grill until done, 3 to 4 minutes more for medium-rare, depending on thickness of meat and heat of grill.
Transfer steaks to a cutting board and cover loosely with foil. Let stand for 5 minutes, and then slice and serve.