From an online description, it does appear to have an intergrated barrel selector.
Compact and easy to maneuver, the Maverick HS12 over-and-unders feature 18.5� matte blue finished barrels, plus handy receiver mounted and under-barrel Picatinny rails ready for quick and easy attachment of sights, lights or other accessories. All Maverick over-and-unders are designed with dual locking lugs for a solid lock-up of barrels to receiver, and feature an ambidextrous thumb operated safety and integrated barrel selector, located on the top tang for convenient, easy-to see operation. Specifications: - Gauge: 12 - Chamber: 3" - Barrel Length: 18 1/2" - Rear Sigth: Slot - Front Sight: Fiber Optic - Choke: Cylinder Bore - Overall Length : 36 1/2" - LOP: 14 1/4" - Finish: Matte, blued - Stock: Black Synthetic - Weight: 6 1/4 lbs