What are these devices? WCML

What are these devices for please? On the WCML, fast side, two south of Kings Langley, two south of Bushey and two north of Harrow & Wealdstone. There may be more.
They always seem to be facing each other in pairs and some have more modern looking windmills attached so guessing they're still in use whatever they do.

Current guesses; vanity mirror for drivers at 125mph. Mobile phone signal obliterator. Upside down solar panels deviating from specification. Some very poorly positioned DOO monitors.

(Sorry for the rubbish photos. It's really hard to photograph from the class 319 rattler at 90mph in the rain.)

Thanks!!

Low adhesion warning signs. Rarely used nowadays but they can be enabled by the controlling signaller in the event that exceptionally low rail adhesion (now called reportable rail adhesion) is reported.



http://www.railsigns.uk/sect23page1/sect23page1.html

Thanks! All makes sense now!