Cut rosemary sprig into 2 (2") pieces. Strip leaves from bottom half of each piece. Poke 2 holes on top of maraschino cherry with a toothpick. Insert rosemary sprigs into each hole. Insert toothpick through cherry, slightly askew from the center to avoid the pit.
Fill a Collins glass with ice, then add Coca-Cola, rum, and cherry juice. Gently stir to combine, then garnish with prepared cherry.
