What martial arts do prison guards/police/security guards/bouncers train in and recommend?

Any martial art is good for law enforcement, but most prefer to learn grappling arts that involves joint locks, pins, take downs, throws, trips, and sweeps. Remember police officers job is to restrain someone and bring them into custody, its not a street fight or a competition of two people exchanging blows. In fact any unnecessary strikes might even be deemed excessive force. Officers pratice arts like Aikido, Hapkido, Judo, and Jujutsu because they involved lots of grappling and submission moves. They learn wrist locks, arm and leg manipulations, joint locks, and pins, ideal for an officer trying to subdue someone and get then into handcuffs.