It's no secret that Shanghai's streets are swarming with illegal taxis. Just last week I was in Jing'an Temple and I hailed what I thought was a regular taxi. It even had the official logo of a well-respected local company.

It was only when I settled into the back seat that I suspected something was amiss. There was no partitioning glass between the driver and the front seat and, perhaps more crucially, no annoying television monitor attached to the back of the seat. But I put these thoughts aside and told the driver my destination: Sichuan Road North.

He informed me he had never heard of any such road. He then turned on his GPS navigator, in an attempt to locate this elusive thoroughfare. He told me we would have to make a left turn at the Bund in order to go in the direction of Sichuan Road North. Having made this journey countless times, I told him that wasn't correct. But because he didn't know the way I normally take, we settled on traveling the way his GPS outlined.

The result was that I paid 5 yuan more than I normally would. And when I offered to pay by transport card, the driver told me that he could only accept cash because he needed the money to "fill up on petrol."

I understand why some drivers would like to operate as a "taxi" without actually being affiliated to an officially-recognized taxi company. They want to avoid the expenses that come with being a properly-regulated cab. But to passengers this is dangerous, because passengers have no idea who the taxi driver is, and what their motive for picking up passengers actually is.

So how do you spot a fake taxi? Drivers have told me that one sure way is to look for a hand-sized blue sticker on the right side of the windscreen that is entitled 警民提示 (which means "a reminder from the police"). Below this are several tips on how to travel safely in taxis, including what to do if you think you have spotted an illegal taxi.

"Every cab firm gets only one copy of this sticker for each car, so it is a guarantee that the vehicle must be a genuine taxi," a driver from Qiangsheng Taxi Company told me.

The police advise citizens to call 110 if they believe they have encountered a fake taxi. It is in these vehicles that passengers are regularly overcharged, and if you are a person traveling alone, who knows what might happen. And if you do suspect you have traveled in an illegal taxi, it is a good idea to take down the license plate number and then report it to the nearest police station as soon as possible.