Several days before Uighur demonstrators gathered in the streets of the northwest city of Urumqi last Sunday in a protest that began China's bloodiest bout of civil unrest for 20 years, secret signs started appearing in taxi windows.
Local security chiefs missed the signals. The clues were important because they were alerting Uighurs in the capital of Xinjiang province to demonstrate against the Han Chinese.
The signals told the Uighurs to avenge the racially motivated killings of two Uighur migrant workers that had occurred last month in a toy factory in southern Guangdong province, triggered by rumours that they had raped several women.
As a result the authorities were caught off guard when the protests erupted, amid erroneous stories that the killers of the Uighurs