This signal controls trains leaving Southampton Maritime Terminal westwards towards Weymouth or Salisbury. It doesn't see much use as most container trains leave the terminal from the other end and head towards Eastleigh.
<a href="//commons.wikimedia.org/wiki/User:Geof_Sheppard" title="User:Geof Sheppard">Geof Sheppard</a>
CC BY-SA 3.0
<span class="int-own-work" lang="en">Own work</span>