Not a milepost. The oddity of this particular Rowe style post has been explained at <a href="//commons.wikimedia.org/wiki/File:Rowe_type_milepost_in_Cardiff_Bay_-_geograph.org.uk_-_622726.jpg" title="File:Rowe type milepost in Cardiff Bay - geograph.org.uk - 622726.jpg">622726</a>. The Welsh language arm seems to have been redirected since that photo was taken in 2007.
<a rel="nofollow" class="external text" href="https://www.geograph.org.uk/profile/11413">Keith Edkins</a>
CC BY-SA 2.0
From <a rel="nofollow" class="external text" href="https://www.geograph.org.uk/photo/1375637">geograph.org.uk</a>