In DC most, if not all Taxis have “Call 911” on the little white “On Duty” bulbs on top of their cars. Why is this? Can you really call 911 for a taxi in DC or do they mean Call 911 for emergencies? Why advertise this if this is the case?
Here are some pics I took in DC the other day:
WAG: When the driver’s in danger (carjacking, maybe robbery), they can hit a switch that turns that light on to alert others to call 911.
Montreal city buses have something similar.
Some people on the web seem to think that’s the cab company’s phone number, but I found this sign manufacturer who says:
http://www.marvintaxiadv.com/pages/2side.html
This fits with Bambi Hassenpfeffer’s theory.
You know that “TAXI” sign on top of the cab? The way those are used is that if the light is “ON”, the cab is available for hire, and if it’s “OFF”, then the cab is occupied (carrying a fare) and thus unavailable.
According to the cab drivers I’ve spoken with, the traditional method of alerting police that a cab driver was in trouble was to leave the light “ON” while carrying the troublesome passenger. The idea was that a passing police officer would see that the light was on and there was a passenger, and that was the officer’s cue to pull the cab over and assess the situation. These same drivers told me they could be ticketed by the officer for leaving the light on when they had a fare but there was no trouble, which suggests this is codified in taxi regulations.
I suppose adding the “Call 911” both simplifies the system and gets the general public involved by alerting them to call 911 instead of the cabby having to hope a cop spots the light.
It’s the mobile version of a silent panic alarm. Hopefully with available technology, a coupled GPS would indicate the cab location to assist law enforcement.
I’ve ridden in DC cabs. I figured that the sign was there because an accident was pretty much inevitable.
In DC cabs, forget GPS. You’re lucky if steering wheel technology has been installed.
I asked the same thing six years ago: ‘Call 911’ On top of taxi cabs.
The only ones I recall seeing were a light on the back of the car, with a sign saying to call 911 if you see the light on or flashing (I don’t remember specifically). It seems like the ones in the OP wouldn’t be all that useful, since people just always see them, so nothing registers if there happens to be some sort of light signal along with it, that most people couldn’t be expected to know.
I see now, duh ! I didn’t even think about that, an alert system. Pretty good idea ! Damn, I guess you learn something new everyday. Thanks !
That’s the quickest way to catch a cab! 
Why do Taxi cabs in DC have “Call 911” on top of them?
Because if it was on the bottom you wouldn’t see it.
Because calling 119 makes no sense at all?
They come out and cause an emergency?
Unless you live in China, where 119 is the 911 #.
In Russia, 911 calls YOU!
