Warrants are typically issued by courts and are directed to the Sheriff, Constable or a Police Officer. The warrants issued by a court normally are search warrants, arrest warrants, and execution warrants. A typical arrest warrant in the United States will take the approximate form of:
"This Court orders the Sheriff or Constable to find the named person, wherever he may be found, and deliver said person to the custody of the Court."
The law enforcement officer in question will have to provide some evidence.