The arrows of indecision clearly looks a safer bet than doomed NR's back of a fag packet logo...
UPDATE: This from Our International Correspondent (and others)...
The Met Rly/GCR boundary sign at Mantles Wood is very smart, and even the proportions and perspective on the "BR" double arrow are right, so unlike Banbury and other piss poor examples see Eye Passim.
But why is this sign so nice, when usually for NR any old thing will do?
Because, to judge from the typeface and colours, it isn't an NR sign. It's a TfL production.
The opposing sign which would be the responsibility of NR - "You Are Now Leaving Coucherland - Use the SPT to ask a Grown Up before passing this point" - is probably not nearly as smart, if it exists at all.