SEOUL • Fans are taking ad-vantage of Seoul's subway stations to show support for their K-pop favourites.

Travelling around the South Korean capital on the subway, commuters will often see enormous advertisements in stations that feature fan messages to K-pop idols.

As groups like BTS stake out a more prominent foothold on the global stage, at home in Seoul, they have already won the war for affection in public transport hubs.

At Hongdae Station, which has more K-pop-inspired advertisements than any other station in Seoul, people stop to take photos of the colourful advertisements, typically placed to celebrate idols' birthdays or anniversaries.

Aya, a fan from Japan, was happy to find a fan-funded advertisement with a message for BTS member Jimin at Hongdae Station to mark his 24th birthday.

"I love Jimin the most from BTS and I find it interesting since we don't have anything like this in Japan," Aya said.

The number of such advertisements is on the rise, according to data provided by Seoul Metro.

The figure had reached 1,576 as of September this year, a sharp increase from 2014, when there were only 76.

The show of affection has paid off, with the stars sometimes showing up at the station to pose in front of the advertisements for photographs to show their appreciation.

K-pop platforms like Click!StarWars and Fandom School are riding on the trend, providing services such as fund-raising and polls to make it easier for people to take part in fan activities.

Seoul Metro, which is losing billions of won each year despite serving millions of passengers daily, is happy for the extra income.

Depending on the location, it can cost from 1.5 million won (S$1,830) to 4.5 million won to put up an advertisement for a month.

Not all advertisements are acceptable to Seoul's transport authorities, however, especially since new standards were put in place in June.

Last year, Seoul Metro announced plans to remove all plastic-surgery advertisements by 2022, after facing criticism for promoting narrow beauty standards.

Political advertisements also face stricter rules, so much so that a birthday message for someone like President Moon Jae-in would have to be turned down for violating rules on maintaining political neutrality.

THE KOREA HERALD/ ASIA NEWS NETWORK