1. Blend soy sauce, vinegar, syrup, garlic, 1/2 teaspoon salt, and 1/2 teaspoon pepper in a blender until smooth. Toss steaks with mixture. Marinate at room temperature about 15 minutes.
2. Prepare a grill for direct-heat cooking over hot charcoal (high heat for gas); see grilling procedure.
3. Discard marinade and pat steaks dry.
4. Oil grill rack, then grill steaks, covered only if using a gas grill, turning occasionally, 6 to 8 minutes total for medium-rare. Let rest on a plate, uncovered, 10 minutes.
5. Cooks notes: Steaks can be marinated up to 8 hours. Steaks can be cooked in a hot oiled 2-burner grill pan over medium-high heat.