In September 2014 protesters (mainly students) took to the streets of Hong Hong Kong to demand the right to elect its own leader in the 2017 elections. Hong Kong is a part of China, but, when the British returned the Colony to China in 1997 China agreed that Hong Kong would be allowed to have a limited democracy until 2047.
When the Chinese Government announced that they intended to choose the candidates for the next election the people were upset and took to the streets to protest. They set up camps in several of the business districts in an attempt to disrupt the business of Government. The Government became annoyed by the disruption and although the people were peaceful they ordered the police to use tear gas to make them disperse.
The protesters shielded themselves from the gas with umbrellas, which are plentiful in Hong Kong because of the climate. The umbrellas became the symbol of the protest. Instead of the gas dispersing the crowd it made the people more determined to continue the protest.
Flyer being distributed by protesters. Click to enlarge.
Examples of postcards distributed by protesters