Who is Private Rod?

You've probably seen this sign on the Tube. Specially if you've been at Embankment station. Paul Clarke asked me to explain who or probably what Private Rod is. It's the sign on a door at the London Underground platform there.


Does anyone know? What I didn't know, is that he also has his own Facebook page (thanks Quartistice) and no one seems to be any the wiser there.

Someone please put us out of our misery and explain.