Whisk together the rum, salt, pepper, cinnamon, powder, oregano, sage, vinegar, and lemon juice in a bowl; pour into a gallon-sized, resealable plastic bag. Add the onion and steaks to the marinade. Seal the bag, squeezing out as much air as possible. Allow to marinate in refrigerator 3 to 4 hours.
Heat the barbecue grill and sear steaks to your preference. Depending on thickness, about 4 minutes per side for medium rare.