It's the thing on the left side (when seen from the front) that says "Kalart". If you look into it from the back (there's only one window on that side), and move the focus knob on the front bed, you should see a double image in the center (will look yellowish) that, when matched up, tells you that the camera is "in focus" for the object in the RF.

When the coating on the internal elements degrade, the double image becomes very faint, and hence difficult to tell when you're actually in focus. A good RF will have a clear second image (that shifts around up & down) when you move the focus knob, and will be clear when it aligns with the actual image.