Having served 2 tours at Lyneham between 1984 and 1991 I seem to remember someone telling me about a large aircraft mural on the wall in the scheduled servicing hangar tea bar. The description given above does sound familiar.
I also remember being told about another large sign on the same wall behind the tea bar counter which informed the users of that fine establishment that it also doubled as the Loadmaster OCU.
All before my time of course!
BB