Say you want to go somewhere along the route to "Circle" (Accra's central bus station). You stand at the side of the road and make a circle in the air with your finger. You wait until you see a tro-tro operator (or "mate") making a similar sign out the window, yelling "circle, circle, circle" to indicate its direction. He sees you. The tro-tro stops. You get on. And away you go. A simple system once you understand. Maddening if you don't.