Signs are a means of traffic control. MSHA recommends that you use signs that can be interpreted by most people, and that are easily understood. For example, the sign in the upper left corner means "no left turn." The upper middle sign is "yield." It doesn’t say yield but we know it’s a yield sign because of the triangular shape. The next one is a sign warning against "falling rocks." The lower left sign shows that they want people to travel from the right-hand side of the road and start driving on the left-hand side. They want to change to "left-hand traffic." The lower middle one is "stop ahead." And, of course, the lower right one is a "10% grade."