Emails that i forgot to post here:
Alistair:
Good morning, thank you for contacting the Definitive Map Team. I have looked on the system and cannot see any closure notices for this path. Due to drafting errors on the original Definitive Map
 there is an acknowledgement that this path is offline and requires a Definitive Map Modification Order (DMMO) to correct it, that will be put in the system and acted on when resources allow (see attached plan). Looking at your attached picture my assumption
 would be that the sign is in place just to advise walkers that the path is not a through route, ie it doesn’t link up with any other path and is therefore not part of the South West Coast Path. I am not familiar with this specific area so I have copied in
 Katie Black, the Senior Ranger, who has a much greater knowledge of this area.
Katie:
I was forwarded your email and the answer given by Alistair is quite correct, the sign is to indicate that the footpath is not the Coastal Path, there was also a sign saying no through route, but
 that seems to have been removed over the summer. 