1. Heat grill to medium-high heat. In a bowl, whisk together vinegar, oil, garlic, thyme, mustard, 1/8 tsp of the salt and 1/8 tsp of the pepper until well blended. Set aside.
2. In another bowl, mix together beef, beaten egg, Parmesan, bread crumbs, remaining 1/2 tsp salt and remaining 1/4 tsp pepper until well combined. Form into 24 meatballs, about 11/2 inches in diameter.
3. Slice off stem and top third of each artichoke; discard. Peel and discard the few top layers of leaves until artichokes are light green. Slice in half.
4. Thread meatballs, artichokes and tomatoes on eight 10-inch skewers. Brush generously with dressing. Grill on medium-high 12 minutes, rotating a few times, until meatballs are cooked through.