RENT YELLOW CAB  are often concentrated in the borough of Manhattan, but patrol throughout the five boroughs of New York City and may be hailed with a raised hand or by standing at a taxi stand. A cab's availability is indicated by the lights on the top of the car. When just the center light showing the medallion number is lit, the cab is empty and available. When the OFF DUTY inscriptions to either side of the medallion number are lit, the cab is off duty and not accepting passengers.