We are all going to suffer after the big electromagnetic pulse has taken out the GPS, even the old furnace dodgers like me who learned to navigate using paper maps. To prepare for this in advance, we should modify the direction signs in a way that the originals didn't think of.
Typically, signs bear
a pointer in one or more directions which tell you where the route is heading and how far away that is (E.g. "PUDDINGTON 4"). But if you are using a paper map, that's not particularly helpful on its own because you don't exactly know where you actually are.
On the sign, however, in a small font, or on the back, there could be a reference number or something like that. I quite like 'What3Words", but if the internet has also been taken out that system may not be working either. So it could be the plain old Ordnance Survey Grid Ref.
Let's start marking them up right now. Or else, after it has happened, don't say I didn't tell you.