"Planetary significator" according to H.L. Cornell

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I have been studying H. L. Cornell's classic "Encyclopaedia of Medical Astrology" and there I found a somewhat puzzling use of the word "significator".

For instance, under the heading "Black Hair"(page 308/309), Cornell lists some astrological features that may indicate black hair, such as: "the Sun in Aries, conjunct or near Cauda"; "Saturn in Gemini, Virgo, Scorpio, Capricorn or Pisces, in partile aspect the Ascendent"; "Venus in Capricorn, partile the Ascendent (dark or black hear)"; "Jupiter combust"; and so on. The meaning of these descriptions is straightforward.

But Cornell often refers to "planetary significators" as well. For instance, under the same heading, he also lists features such as: "the Moon significator in Taurus, Virgo, Scorpio or Capricorn"; "Saturn significator in Libra (a comely brown)"; "Mercury significator in Virgo in the terms of Jupiter or Saturn"; and so on.

What does Cornell means exactly by "Mars (or Saturn, or any other planet) significator"?

It is clear that a "planetary significator" is not the planet itself, since Cornell mentions quite a few cases in which both are clearly distinguished. For instance, under that same heading, "Mars in Scorpio, partile the Ascendent, or Mars significator in Scorpio (black, curly)".

I am acquainted with the concept of "dispositor": so, if the Sun is in Sagittarius, Jupiter is the Sun dispositor; if the Moon is in Capricorn, Saturn is the Moon dispositor, and so on. But I never found the word "significator" meaning "dispositor", and the idea of a planet signifying another planet seems to me somewhat wired. Is this usage common?

If anyone familiar with Cornell's book could explain me what does he mean by such usage (which is fairly common throughout the whole "Encyclopaedia"), I would be grateful.