I found this interesting and it seems a pity the thread deviated so quickly.
I'm familiar with that area too, although I've not been in the last couple of years. It's the type of thing it would be possible to look at without really clocking the to/from: all the mind is registering is the distances and place names. Anyway, I've never noticed it. If it's not unique to that location, then it may be peculiar to some long-gone surveyor in that bit of Northumberland.