Combine the olive oil, balsamic vinegar, artichoke hearts, sugar, salt, dry mustard, bay leaves and garlic in a bowl and mix well. Add the shrimp and onion and toss to coat well. Marinate, covered in the refrigerator for 3 to 10 hours. Drain the shrimp, reserving half the marinade and discarding the bay leaves. Place the shrimp and reserved marinade in a serving bowl. Garnish with lemons and olives. Set in a bowl filled with ice and serve with wooden picks.