See that thing on the wall?
That is an etiquette bell. You find them in many public bathrooms all over Korea. If you press the button, it'll play a little music or white noise, like water rushing or static. It's quite polite!
Just another example of the delightful random things we have in Korea that we don't have back in the States.
[side note: see that gigantic bathroom trash bin? it's huge cause NO ONE THROWS TOILET PAPER IN THE COMMODE. Korea thinks it's supposed to go in the trash. Maybe there aren't as many stopped toilets up in this country, but FOR GOODNESS SAKES, that's unsanitary. end side note]