Make the marinade: Combine the soy sauce, cola, brown sugar, garlic, pear and sesame oil in a large bowl. Stir together with a whisk or fork until the sugar is dissolved and the garlic is distributed evenly.
Marinate the short ribs: Add the short ribs to the marinade and massage it into the beef. Cover and let marinate in the refrigerator for 1 to 4 hours.
Heat a grill pan or grill over high heat for at least 5 minutes. Wipe the grill pan or grill grates with a lightly oiled towel right before cooking to remove any char and debris. (This will give you great grill marks and help the beef from sticking.) Working in batches, pat any excess marinade off the short ribs and grill in a single layer for 4 minutes per side, or to your desired doneness. Remove from the grill and garnish with the scallions and sesame seeds.