I’ve driven past a sign just like this one hundreds of times, but it took me in one of my thinking moments to appreciate how effective it is at communicating a message that is usually explained in terms of metres and car lengths (like this one from the Merseyside Road Safety Partnership).
It’s not the most attractive thing you’ll ever see, but its simplicity is what makes it effective. The message is very simple, what you see on the sign is what you should see ahead of you.
In case any members of the police are reading, I should point out that this picture is not one that I took!