The laws of restraining order vary by state. In Michigan, for example, a restraining order is called a personal protection order (or PPO). It can be filed in any county of the state, but is only effective once it is served on the respondent (the person to be restrained). Then it is put into the police database (LEIN) where law enforcement has that information about you whenver they run your name. A good investigator should be able to tell you if a restraining order has been filed against you, unless your state has rules regarding confidentiality of filed restraining orders.