Surrounded by riot police and silhouetted against the fog of tear gas, the umbrella is what sets the photograph above apart.

The image, which shows a protester hoisting a parasol at ongoing protests in Hong Kong, quickly became known as the "The Umbrella Man" on social media.

Without a word, it explains how this quizzical yet ubiquitous object has become the symbol of what is being called the greatest political challenge to China in a quarter century.

By comparison, the Tiananman Square protests of 1989 were immortalised in the image of a lone protester defiantly standing in front of one of the People's Republic of China's tanks, with a single hand held forth in opposition.

The picture of a protester with an umbrella might not be as emotionally evocative, but both demonstrate how an image can encapsulate a moment in history and a symbol can define a political movement.

Hong Kong's protesters are not the first to popularise the umbrella as the dissident's accessory of choice.

"The Umbrella Revolution" in Latvia, 2007 [Reuters]

Latvia's anti-government protests in 2007 became known as "The Umbrella Revolution," after thousands of people braved inclement weather calling on the country's then-Prime Minister Aigars Kalvitis to resign.

Kalvitis was the country's longest-serving prime minister, but his name was sullied after he sacked a leading anti-corruption investigator – a move that was seen as politically motivated.

He stepped down a month after that wet November during which the protests took place, but it was the sea of multi-coloured umbrellas that is remembered most vividly.

China's government has so far signaled it is unwilling to concede its oversight over the nomination process in Hong Kong's leadership elections, scheduled for 2017, which has sparked the protests.

Demonstrators are promising continued escalation in the scale of their sit-ins and in their plans for civil disobedience.

A police crackdown on Sunday that launched pepper spray and tear gas against protesters left many shocked and angry.

Protest leaders say they have taken a defensive posture throughout their campaign, but some of those attending the demonstrations have committed acts of violence.

It is clear that the umbrella is being used as a figurative shield as well as a physical one, adding to the image of a largely peaceful movement and serving as a symbol of alleged political oppression.

Source: Al Jazeera