These signals control trains heading westwards through Taplow station (they are situated between the station and the bridge over the A4 road. The one on the straight post controls the main line closest to the camera; the cantilvered one controls the relief lines used by slower services. They have four-aspect LED signal heads with one lamp showing the usual red-yellow-green aspects and the second one being used when it is necessary to show a double yellow signal.
<a href="//commons.wikimedia.org/wiki/User:Geof_Sheppard" title="User:Geof Sheppard">Geof Sheppard</a>
CC BY-SA 4.0
<span class="int-own-work" lang="en">Own work</span>