A searchlight signal has a rather narrow beam. Because of this, when you are close to the signal outside of its main beam, it is difficult to see the aspect the signal is displaying. A deflecting or close-up prism casts a small amount of light to the side or down at approximately 40 degrees, depending on its rotation, which enables a person near the signal to see its aspect.

In the H style searchlight signal and most other railroad signals using an outer doublet lens with concentric prisms, the close-up prism is molded into the center or bullseye of the lens.

In the style H-2 searchlight signal, the close-up prism is located between the inner and outer doublets.  It can be accessed by removing a hand hole cover on the top of the neck of the H-2 case.  The area of close-up indication can be adjusted by rotating the close-up prism in its holder.

Above.  With hand hole cover removed, the close-up prism can be seen in its holder.

Above.  Hand hole cover.

H-2 signal case.  With the internal unit removed, the close-up prism and holder are clearly visible.

Above.  Close -up prisms - front and back sides.