The "tunnel ahead" sign always struck me as particularly pointless. Who needs that sign? Surely if you're driving towards a tunnel, the enormous tunnel itself is the indication you need that you're heading towards a tunnel?

Honourable mentions for "humps ahead".

Those are for truck drivers and those carrying dangerous goods The Blackwall Tunnel in London has those signs starting something like ten miles south (ie on the edge of the city!), to try an ensure such vehicles don’t reach the tunnel unwittingly and force it to be closed.

I mean the one they put directly in front of a tunnel, with the tunnel picture inside a red triangle. I live quite near Blackwall tunnel and haven’t seen it any of those on the approach. The ones you’re talking about are, I believe, red circles containing the actual restrictions which are, of course, fine.

Also strictly speaking, the restrictions, even if those red circles were combined with the tunnel warning, the tunnel warning is still irrelevant - you’d have to follow those restrictions whether or not there was a tunnel.

We have these in the US too because we have a ton of Semi's and big rigs. They can get stuck. Usually the signs include the clearance too, like 12'8".

There's some funny videos online of trucks getting a haircut from these. So seems necessary to me.