For Olive Mayo, in bowl combine mayonnaise, olives, dill, and garlic. Cover; refrigerate up to 1 week.
Brush steaks with oil. Combine rosemary, salt, and pepper; rub on steaks. Let stand at room temperature for 30 minutes.
For charcoal grill, place steaks on rack directly over medium-hot coals. Cover and grill 9 to 11 minutes for medium rare (145 degrees F), turning once. (For gas grill, preheat; set to medium-high. Cover and grill as above.)
Sprinkle steaks with fresh rosemary; cut in serving portions. Serve with Olive Mayo and Herbed Potatoes and Squash. Serves 4 to 6.