A MS1 central reservation or 'post' mounted signal that is displaying a ice warning. While the law and documents provide for this aspect, design documents don't depict a lamp layout, so this is a theoretical design of the lamp layout, due to a lack of existing documentation depicting the lamp layout. 
The amber lamps flash in pairs from top to bottom.
This vector image includes elements that have been taken or adapted from this file:
Adapted from Mauls.

UK Government