Historically going back you also have to remember that not much over 100 years ago, before the rise of the motor car, that most roads were not signed, and only the locals used them.
In fact if you go into the lanes to the west of Hitchin you will find many of those lanes still have no signs and you have to know how they connect or be following your GPS.
In France at the end of the 19th century there were no road signs or directions at all. It was Michelin who, having developed excellent tyres, had to find a way for tourists to use their vehicles and wear out their tyres (so that they would need to replace them). This meant drawing maps and guides so that people would know where they might like to go - but there were no signs on the roads so Michelin had to put up signs as well! Perhaps if there was a bit of a commercial incentive nowadays the paths and the signage would be much better (as we find in places like the Loire valley).
Incidentally some Michelin road signs still exist. I used to photograph interesting ones if I had a camera to hand. I don't know if the Michelin guides were aimed more at cyclists at first or at motorists - I don't think Michelin cared either way so long as they sold more tyres! Now did anyone think in the same fashion in early 20th century UK?
I have never managed (admittedly not had a lot of experience trying but more than not at all) to follow ant british cycle route. I always miss a sign somewhere (or perhaps the sign was already missing!)