In country parts of the United States, RR on an address means Rural Route. The post office used to — and in some places still does — deliver mail along numbered routes in the countryside, instead of to a named street in a town. So an address might look like RR 2 Box 14: the second rural route, mailbox number 14. It tells the carrier which round to drive, not a city street name. You will not see this on a London or Taipei address. If you write to a farm or a house far from town in the US, you may still meet RR. Though actually, many of those old routes have since been given ordinary road names, so RR is less common than it once was, but it is still the meaning in American country addresses.