Tube escalators
In busy London tube stations tourists unfamiliar with the etiquette (stand on the right, walk on the left) are often causing congestion.
I proposed "Transport For London" to apply stickers indicating the 'walking' and 'standing' lanes. A solution that transcends languages and cuts through the jumble of visual messages around.

Update: TFL started testing this in a few tube stations

Read some press about it here and here.