Thought this might be something to do with the Wombles (Overground,
Underground, Wandering Free - or something like that).
But I do find a lot of people seem confused by the fact that the Underground
runs overground for much of its lengths. And at West Hampstead, for instance,
with three stations to choose from, some people do get confused as to what line
runs where. Whether the signs you describe will help, I don't know, but without
going into whether people are "stupid", the system is confusing, and a lot of
people do get confused.
And then there are the American tourists who look mystified when I tell them
that the bus they have decided suits them, with a "N" before the number, is a
Night Bus. "But it's night now!", one protests - it is 6.30pm OK, so
Americans are in a category of their own - like the ones I was directing to a
National Express for "Leicester" before I realised they really wanted to go
Leicester Square, or the two that asked for "Buckingham", but meant the palace.

Still, Londoners are not always clever, either.