Hailing a Cab. The act of flagging down a cab is called "hailing"; there's not much to it, just stick out your arm and pretend you're the Statue of Libery. When the numbers on the roof of the cab are lit, it is available. Yellow Medallion cabs are the only ones authorized to pick up hails. Avoid "gypsy" cabs at all costs. These are regular cars that will take you from place to place; they usually cost more than cabs and aren't as well regulated (or as safe).