If you walk through Piccadilly Circus station, you might just see the seven members of K-pop band BTS smiling at you on one of the station's billboards.
Fans of the group (often referred to as ARMY) pooled their resources to purchase £2,000 worth of advertising space in order to commemorate the eighth anniversary of the group's debut.
"They're a way for UK ARMY to celebrate with BTS," Lorraine, a representative of the BTS UK ARMY Unite group, told the BBC.
It's part of a global effort by international fans of the group to purchase as many posters as possible around the world to mark the milestone.
"Since 2017, we have fundraised for anniversary billboards in London, Manchester and Dublin and we are so grateful to ARMY from all over the world that have donated to make this happen each year! " Lorraine said.
Our BTS Anniversary billboard is in Piccadilly Circus Underground Station, London! 🇬🇧— BTS UK ARMY UNITE ⁷ 🧈 (@BTSUKUNITE) June 12, 2021
Happy 8th anniversary @BTS_twt! 💜#BTS8BeautifulYears #BTS8thBirthdayProject #8YearsToInfinityWithBTS pic.twitter.com/A2ACmk7e2A
It's not the first time that BTS fans have bought billboards to show their support for their favourite group. In 2017, Chinese fans of the group bought adverts in New York's Times Square to celebrate the group's fourth anniversary.
In 2019, a Korean government agency found that global fans of Korean popular culture, referred to as the K-wave, number some 89 million in 113 countries.
These K-wave fans are now finding ways to show their appreciation of their favourite actors and musicians - often described as idols.
Saying thanks with food trucks
"Food trucks have been a fan tradition in the Korean entertainment industry for a long time," a representative for Edelweiss Philippines, a fan club for Crash Landing on You actors Hyun Bin and Son Ye-jin, told the BBC.
"Not sure who started the trend but fans of both K-pop stars and Korean actors usually send one during filming to cheer for their idols and show support to the cast and crew," they said.
The fan club teamed up with other groups in South East Asia to send Hyun Bin a coffee cart last March, spending around $2,800 (£2,016).
Fan groups have to apply for a slot from the agencies and can then arrange the cart. They design the banners and stickers that are used by food trucks and discuss how many members of crew will be on site that day to ensure there is enough for everyone.
In pre-Covid times, several fans were allowed to attend the site to assist the operators of the truck and ensure the process runs smoothly.
The fan group is then given updates from the food truck vendor on how things are going.
"We were told that Hyun Bin personally visited the food truck to get his food and drinks. He spent some time reading our banners and watching the video edit playing on the truck and then said his thanks," the spokesperson said.
Some artists choose to thank fans by posing with the trucks but in this case, actor Hyun Bin is not on social media aside from his agency's Instagram.
Getting your favourite idol higher in the charts
If there's one way to say thanks to your idol, it's by getting them higher in the charts. This is done by promoting the artist's music on social media, requesting radio plays and buying the music, sometimes on multiple platforms.
Other groups host competitions where fans can win items if they purchase music in support of their idol. Some even raise money so that fans who can't afford to buy the music themselves, have the funds to do so.
USA Ahgases, a group dedicated to the band GOT7, is currently finding ways to support members of the group who are currently working on solo projects.
"We are trying to find ways to make them go higher," an admin of the group said. "We have some items like making keychains, lanyards etc, things that Ahgases could use every day".
"I personally do it because I love the boys and love seeing them happy and I love seeing when they update us and they have seen that they have succeeded in the charts," they said.
"We love GOT7 as much as GOT7 loves us. We support one another as much as we can.
"No matter what we are doing, GOT7 always gives us strength".
Raising money for good causes
K-wave fans are known for their generosity, donating to good causes such as planting trees in the Amazon or helping koalas injured in last year's Australian bushfires.
Edelweiss Philippines said it had recently raised money for charities to mark the birthdays of Hyun Bin and Son Ye Jin.
"To celebrate Son Ye Jin's birthday, we donated more than 50% of our birthday fund to Save the Children Philippines because we know she loves kids and she's been involved in child welfare in the past," the spokesperson said.
BTS fans hit the headlines last year after they decided to match the group's $1m donation to Black Lives Matter. They reached their target in just over 24 hours.
The fan collective - One In An Army - which spearheaded the campaign said in a statement: "We stand in solidarity with black ARMY. They're an important part of our family. And we stand with black people everywhere. Your voices deserve to be heard."
Bangtan UK, a group for fans of BTS, has worked with international BTS ARMY groups to help raise money for good causes.
"We also raise funds for charities such as The Justice Desk's Mbokodo project, " Gabbi, an admin of the group told the BBC. "This project is a collaboration with South African BTS fanbases and takes on BTS's Unicef messages of Love Yourself and END violence, with the funds going back to help and protect young female survivors of rape and gender-based violence in South Africa."
"Our events give us an opportunity for it to be known that the UK does have dedicated fans and hopefully gets the word spread around BTS and their music," she said.
"For us all, it's more than just a group of people supporting a K-Pop group, it's people coming together to support each other as well as BTS. Therefore, for us BTS means family."