While fighting crime is primarily limited to the police, a number of people from the general public look for police related collectibles, for different reasons. For example, items like police uniforms, badges and hats can make for very convincing fancy dress costumes.
Police handcuffs are effective tools in training novice security personnel. Buying ex police cars and equipment can give you a first-hand feel of men and women in uniform. Whatever you do, make sure you do not break the law.