All the 3s....San Francisco.
There are a few things that you can do in order to grab one of the hundreds of San Francisco taxis. The first step is in knowing if a taxi is available or not.
If the top 'TAXI' light on the hood of their car is on, then the taxi is open. Make sure it's the TAXI light and not the surrounding lights on their hood. Some taxis have lights surrounding their TAXI light and they will shut off just the TAXI portion of the light when they are full.
To hail a San Francisco taxi, make sure that you are far enough out for them to see you. The idea is not to just leave your hand up, but to try to engage with the driver to let them know you are seeking a San Francisco cab.