Being a taxi driver is actually very dangerous. It belongs to the group of occupations with the highest murder rates. The average murder rate is 0.0000037% whilst it is 0.000074% for taxi drivers. That means it is 20 times more likely for a taxi driver to be murdered as compared to any other person.Due to this, most taxis have built in silent alarms that can be triggered. These can come in all shapes and forms but are definitely recognizable. If you see any sign on a taxi start to flash, you should a.s.sume that it is the driver signaling for help. Unless you are in a foreign country where there could be a misunderstanding (it also really depends on the time and location) [if you are in the middle of the city during the day a local should notice it], you should notify the police. Better to be safe then sorry as there could be a life on the line.
There once was a group of students who took a taxi trip around the world to raise money for a charity. They paid over $100,000 on just the taxi ride alone, however they only raised $25,000. That is a large sum, but they wasted quite a bit with their trip. Along the way they ran into alot of problems and were even arrested on multiple occasions.
Back in Febuary of 2017, almost a million British pounds were found on the back seat of a black cab in London (the cash was found by the police).