Why Seoul's Subway Stations Are Full of Birthday Ads for Pop Stars, and How a Fan Puts One on the Wall

Step off the train at Hongdae Station and somewhere between the platform and the ticket gates you will meet a very large face, a date, and the words "Happy Birthday". It looks like an advertisement. It has the frame and the lighting of one. But there is nothing for sale, and the company that paid for it is not a company.

A fan paid for it. Usually many fans, pooling money, weeks earlier. This is one of the most visible habits of Korean fandom, and it is also one of the easiest to misread from outside, so this article follows a single ad from the idea to the wall: who sells the space, what it costs, how long it takes, and what a fan abroad can actually do.

What you are looking at

Fan-funded idol ads are not a side note in the Seoul subway. According to figures Seoul Metro released, the number of idol ads on the network went from 76 in 2014 to 2,166 in 2019, out of 10,468 advertisements that year, so about one in five. Korean coverage of the growth puts much of the credit on Mnet's Produce 101 audition series, where viewers' votes decided who debuted and fans began buying subway space to ask for them.

A Korean news series published in September 2026 counted 12,433 idol ads that passed review in 2025 and 8,012 in the first eight months of 2026. Do not line that number up against the 2019 one to calculate growth. The two count different things, and I have not been able to confirm how each was measured. What both say is the same: this is routine now, not a curiosity.

The occasion is mostly a birthday. Debut anniversaries and big career moments get ads too, but the birthday is the fixed date on which every fan club in the world is thinking the same thing. One of those September reports, about a single member's birthday, counted ads at 24 stations.

Reading one of these ads

Once you know what to look for, an ad stops being decoration and starts being a message with a fixed shape.

There is a photograph of the idol. There is the name. There is the date, which is the reason for the whole thing. And there is a line of text, often a version of "Thank you for having been born" or plain "Happy Birthday". The ad pictured below reads "Happy WooSeok Day" in English and, in Korean, "Wooseok-ah, happy birthday". The "-ah" on the end of the name is the casual, affectionate way to address someone you are close to, and it sets the tone of this one.

Read it as addressed to two audiences at once. To the idol it says thank you. To every other fan who walks past, it says we were here.

Who actually sells the wall

Two facts about the seller explain most of what surprises people.

The price is not set by the subway operator. Seoul Metro leases its advertising to agencies that win the space through a bidding process, and those agencies set the rates. Seoul Metro has said it does not get involved in the price of individual ads.

Money does not guarantee a place. Every ad goes through Seoul Metro's own advertising review committee. If it fails, a higher offer changes nothing. This is the reason a fan ad that looks like a fan ad has usually been checked by a body with rules about what a public wall may say.

Together these mean the market is a lot like renting a billboard anywhere else, with one difference: the buyer is a group of strangers who have never met and all love the same person.

How one ad gets made

This is the practical part. The order is the same however large or small the ad is.

1. Pick the wall. Stations are not equal. The busiest ones cost the most, which is exactly why fans want them. Hongdae Station carries more idol ads than any other station in the city, and it has both the tourists and the teenagers to a degree few others do. Other favourites are Gangnam, Samsung and Hapjeong on Line 2, Apgujeong on Line 3 and Myeongdong on Line 4.

2. Price it. The last public numbers I could find are from February 2022, when Korean reports described ad prices at major Line 2 stations jumping by at least 50%. For the standard 4.5-metre-wide format, Samsung went from about ₩4.5 million to about ₩7 million. Gangnam and Hongdae were around ₩7 million. Euljiro 1-ga, Konkuk University, Jamsil and Gyodae were around ₩5 million, Wangsimni, Seolleung and Yeoksam around ₩4 million, and Ewha Womans University, Yeongdeungpo-gu Office and Seocho around ₩3 million.

Those are four-year-old figures. For a current one, the booking listing shown below offers a one-month "wide colour" ad panel at Sadang Station for ₩2,997,500, with production and VAT included. That is close to the ₩3 million the 2022 list gave for its cheapest stations, though I cannot say the two formats are identical. It is a single listing, not a price list: booking services price the same kind of ad differently from one another, so a second service can quote another figure for the same wall, and I found no published current rates for the prime stations. Treat all of this as a way to see the shape of the market, not as a quote. The shape is the useful part: a prime station costs more than double a quiet one, and fandoms pay it anyway.

3. Design it. The ad is a picture, a name, a date and a short message. You either supply the finished artwork yourself or pay a booking service to make it.

4. Send it for review. One booking service that handles these for fans says review can take up to seven days depending on the format, and recommends starting three to four weeks before the birthday. The same service lists two common formats: a large lightbox (400 by 225 cm) that stays up for a month, and a poster (77 by 107 cm) that stays up for three months. Durations and sizes differ by station and by agency, so read these as one service's terms, checked on 30 September 2026, rather than a rule.

5. It goes up, and then it comes down. This matters for anyone who wants to see one. An ad is not permanent. The birthday ad you saw in a photograph may be gone by the time you arrive.

Splitting the bill

Millions of won sound absurd until you divide them. This is arithmetic on the 2022 price for a prime station, not a figure from any fan group, but it shows why the system works.

Split between 100 people, a ₩7 million ad is ₩70,000 each. Between 500 people, ₩14,000. Between 2,000, ₩3,500. A large fandom can afford a prime wall precisely because no single fan pays much, which is what makes a birthday spread across 24 stations thinkable.

A small fandom does the same sum and reaches a different answer. Twenty people cannot comfortably fund a ₩7 million wall, so they book a quieter station, where the same money buys the same message in a cheaper spot. Seen that way, a modest ad at a quiet station is not a failure of ambition. It is a sum that a fan club of that size can afford.

If you are not in Korea

You do not need to be. Several services exist specifically to book ads for overseas fans. They handle the Korean-language conversations with the agency, accept your finished artwork or design one for an extra fee, and confirm the final version with you before anything is printed. A fan gives an idol, a date and a budget, and the service suggests what that buys.

Three habits keep this from going wrong. Ask more than one service for a quote, because their prices for the same kind of ad are not the same. Book earlier than feels necessary, because review and installation are the parts you cannot rush. And decide the budget before the station, because a fan project can quietly become a much larger one when everyone is choosing between a good spot and a great one.

It is also worth saying plainly what this is. You are paying a commercial service to put an image on a wall, and the wall is the message: it reaches whoever walks past.

What about buses and billboards

The subway is not the only wall. Booking services for overseas fans list bus wraps and outdoor billboards alongside station ads, and fans do buy them.

I have left them out of the numbers in this article on purpose. I could find dependable public prices only for subway stations, and quoting a figure for buses or billboards that I could not trace to a source would be worse than saying nothing. If you want one of those, ask a booking service for a current quote and treat that as the price. For everything else here, the subway is where the habit is most visible, best documented, and easiest to go and look at.

If you are just visiting

You can see these for the price of a fare.

• Go to Hongdae Station first. It is the single best place to see many at once.
• Try Line 2 next. Gangnam, Samsung and Hapjeong are the usual others, with Apgujeong on Line 3 and Myeongdong on Line 4.
• Check the birthday, not the station. Ads cluster around the date. Look up the birthdays of the groups you like and plan around them, since the ad you came for might run for a month or three, or might already be gone.
• Mind the platform. These stations are commuter stations first. People stop to photograph the ads, and it is worth stepping out of the way of the crowd while doing it.

Why fans pay for this at all

The obvious answer is that it is a gift. The less obvious one is that the idol is not the main audience. An idol's schedule does not include a walk through Gangnam Station.

The audience is the city. Fans are making the group visible to millions of strangers, and making themselves visible to each other: an ad is proof that this many people care, in the one place where the people who see it are not fans. An anthropologist's 2021 paper in City & Society frames it as fans appropriating subway space and claiming a right to the city. That is a grand way to describe a birthday poster, and it is also accurate.

For a visitor, the ads are the most concrete evidence you will find that the fandom you are reading about is an organised, funded and public thing. It is also the one part of it you can see without buying anything.