As the number of Vietnamese immigrants increases in Taiwan, there are sometimes scary scenes in addition to enrichment of local culture/來自越南的新臺灣人越來越多。在欣賞越南特色之餘，有時也會碰上觸目驚心的場面：
I do not think they know the meaning of this gesture.
According to Wikipedia:
V sign as an insult
The insulting version of the gesture (with the palm inwards) is often compared to the offensive gesture known as "the finger". The "two-fingered salute", also known as "The Longbowman Salute", "the two" and as "The Tongs" in the West of Scotland and "the forks" in Australia, is commonly performed by flicking the V upwards from wrist or elbow. The V sign, when the palm is facing toward the person giving the sign, has long been an insulting gesture in England, and later in the rest of the United Kingdom; however, this is quite untrue in America where it is used as a peace symbol; its use is largely restricted to the UK, Ireland, Australia, and New Zealand. It is frequently used to signify defiance (especially to authority), contempt, or derision.
As an example of the V sign (palm inward) as an insult, on November 1, 1990, The Sun, a British tabloid, ran an article on its front page with the headline "Up Yours, Delors" next to a large hand making a V sign protruding from a Union flag cuff. The Sun urged its readers to stick two fingers up at then President of the European Commission Jacques Delors, who had advocated an EU central government. The article attracted a number of complaints about its alleged racism, but the now defunct Press Council rejected the complaints after the editor of The Sun stated that the paper reserved the right to use vulgar abuse in the interests of Britain.
For a time in the UK, "a Harvey (Smith)" became a way of describing the insulting version of the V sign, much as "the word of Cambronne" is used in France, or "the Trudeau salute" is used to describe theone-fingered salute in Canada. This happened because, in 1971, show-jumper Harvey Smith was disqualified for making a televised V sign to the judges after winning the British Show Jumping Derby atHickstead. (His win was reinstated two days later.)
Harvey Smith pleaded that he was simply using a Victory sign, a defence also used by other figures in the public eye. Sometimes foreigners visiting the countries mentioned above use the "two-fingered salute" without knowing it is offensive to the natives, for example when ordering two beers in a noisy pub, or in the case of the United States president George H. W. Bush, who, while touring Australia in 1992, attempted to give a "peace sign" to a group of farmers in Canberra—who were protesting about U.S. farm subsidies—and instead gave the insulting V sign.
Also, in the opening credits for a number of seasons of Buffy the Vampire Slayer, Spike, who is British, is shown using the V sign as an insult to Xander Harris in a scene from the episode Hush.
On April 3, 2009, Scottish football players Barry Ferguson and Allan McGregor were permanently banned from the Scottish national squad for showing the V sign while sitting on the bench during the game against Iceland. Both players were in their hotel bar drinking alcohol after the Scottish defeat to Holland until around 11 am the next morning, meaning that both of the players breached the SFA discipline code before the incident as well, but the attitude shown by the V sign was considered to be so rude that the SFA decided never to include these players in the national line-up again. Ferguson also lost the captaincy of Rangers as a result of the controversy.
Steve McQueen the late American actor gives a British (knuckles outward) V sign in the closing scene in 1970s motorsport movie 'Le Mans'. A still picture of the gesture was also recorded by photographer Nigel Snowdon and has become an iconic image of both McQueen and the 24 hours of Le Mans.
Eric Young a TV news anchor in New Zealand was accidentally broadcast flashing the V sign to a producer off screen after a report on a Rugby match between Auckland and Counties Manukau.
An early recorded use of the "two-fingered salute" is in the Macclesfield Psalter of c.1330 (in the Fitzwilliam Museum, Cambridge), being made by a glove in the Psalter’s marginalia.
According to a popular legend, the two-fingered salute or V sign derives from the gestures of longbowmen fighting in the English army at the Battle of Agincourt (1415) during the Hundred Years' War.According to the story, the French claimed that they would cut off the arrow-shooting fingers of all the English and Welsh longbowmen after they had won the battle at Agincourt. But the English came out victorious and showed off their two fingers, still intact. Historian Juliet Barker quotes Jean Le Fevre (who fought on the English side at Agincourt) as saying that Henry V included a reference to the French cutting off longbowmen's fingers in his pre-battle speech. If this is correct it confirms that the story was around at the time of Agincourt, although it does not necessarily mean that the French practised it, just that Henry found it useful for propaganda, and it does not show that the two-fingered salute is derived from the hypothetical behaviour of English archers at that battle.
The first definitive known reference to the V sign in French is in the works of François Rabelais, a sixteenth-century satirist.
It was not until the start of the 20th century that clear evidence of the use of insulting V sign in England became available, when in 1901 a worker outside Parkgate ironworks in Rotherham used the gesture (captured on the film) to indicate that he did not like being filmed. Peter Opie interviewed children in the 1950s and observed in The Lore and Language of Schoolchildren that the much older thumbing of the nose (cock-a-snook) had been replaced by the V sign as the most common insulting gesture used in the playground.
Desmond Morris discussed various possible origins of the V sign in Gestures: Their Origins and Distribution (published 1979), and came to no definite conclusion:
because of the strong taboo associated with the gesture (its public use has often been heavily penalized). As a result, there is a tendency to shy away from discussing it in detail. It is "known to be dirty" and is passed on from generation to generation by people who simply accept it as a recognized obscenity without bothering to analyse it... Several of the rival claims are equally appealing. The truth is that we will probably never know...—Desmond Morris.