Preheat barbecue to medium-high. Grill lemon and lime slices to char slightly, about 1 min. per side. In a large pitcher, mix tomato clam cocktail, barbecue sauce, 1/4 tsp (1 mL) pepper and grilled citrus, reserving 8 slices each grilled lemon and lime for garnish.
Mix rim ingredients on a small plate. Rub rim of 8 highball glasses with a slice of lemon and dip into mixture to coat. Fill glasses halfway with ice, top up with Caesar and garnish with grilled citrus and fresh cilantro.
For greater smokey flavour, prep this Caesar in advance.