That is the 'Datum Point' for CoG calcs etc.
Ah, that's why I didn't know about it. We never did CofG calculations. I think the assumption was that if you could fit in the seat, the aircraft was under gross and within limits.
A bit different for me today!
That Yellow Band looks more Orange
Probably due to the fact that the second image was scanned from a slide. The yellow in the top picture is how I remember the shade and it looks similar to the yellow in your picture.