In a resealable plastic bag or shallow dish, combine vinegar, sugar, garlic, rosemary, 1 teaspoon coarse salt, and 1/2 teaspoon pepper. Pierce meat all over with a fork; add to marinade, and turn to coat. Let marinate at room temperature at least 15 minutes, or cover and refrigerate up to 1 day.
Heat grill to high; oil grates. Remove steaks from marinade, allowing excess to drip off. Grill steaks 2 to 4 minutes per side for medium-rare. Transfer to a plate; cover loosely with aluminum foil, and let rest 5 minutes.