The coordinate system is defined with x as the axial direction. The y-axis points up to the first rolling element and the angle ψ is positive around the x-axis or clockwise in the diagram on the right (looking in the direction of the x-axis). The angle starts with zero at the first rolling element on the y-axis. Moments are positive if acting around the corresponding axis.
The load is acting on the inner ring (different for track rollers with elastic outer ring), so a positive load in y-direction leads to a loading of the rolling elements on the top as shown in the graphics on the right.