This is one you will see all over the place. They appear right before you come upon a roundabout. A roundabout is a strange street configuration that pushes all the roads in the city (and a few that are visiting from other towns) into a confused junction in the hopes that they will trap foreighners like flies in a pitcher plant. The sign is an instructionas to the proper way to progress through the roundabout. Here is how you do that.

Rule number 1. Always go Clockwise around the roundabout. This is key.
Rule number 2. Always Yeild (or as the British say "give way") to cars that are coming at you really fast through the roundabout.
Rule number 3. Always progress through the roundabout as fast as you can. (You'll need to to be missed by all the other cars tat are also progressing though at breakneck speed.
Rule number 4. (This is the most important rule.) It is absolutely manditory that you go all the way around the roundabout at least twice (preferably shouting “Wee!” out the window as you go) before exiting the roundabout. (Try it! It's Fun!)