The 4th floor in Korea has the same status as the 13th floor does in the US. The pronunciation for "4" is "sa" which is the same as the Chinese character for "death", hence the "F" instead of "4" in elevators. Quite silly really.
<a rel="nofollow" class="external text" href="https://www.flickr.com/people/41894171246@N01">Nam-ho Park</a> from Seoul, Korea
CC BY 2.0
<p><a rel="nofollow" class="external text" href="https://www.flickr.com/photos/namho/3760622276/">No 4th Floor</a>
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<ul><li>Uploaded by <a href="//commons.wikimedia.org/wiki/User:Rybec" class="mw-redirect" title="User:Rybec">Rybec</a></li></ul>