The door even has its own Facebook page, with people wondering whether "Private Rod" reports to Captain Cabinets.
It appears that current London Underground staff don't know why the door's there either. Jon who works for TfL said "I’ve asked around a lot of the usual fountains of knowledge within LU and as yet have not found an answer.
I received two updates today:
1. The staff at Embankment Tube have no idea what the sign means, but did say that behind the door is nothing but a brick wall!
2. There is a similar door at Ealing Broadway, but again the staff there don't know what it is for."
I had heard that it may stand for Rail Operating Department - but they clearly don't do much operating if there's only a brick wall behind the door. Why are there only two of them on the whole network? Unless you've seen them elsewhere!
Any more theories as to who or what Private Rod is?