Why does a crescent moon appear on Chibi-Usa's forehead?


In Episode 60 "Angel or Devil? The Mysterious Girl from the Sky" and episode
64 "In Search of the Silver Crystal: Chibi-Usa's Secret", I noticed a crescent
moon appears on Chibi-Usa's forehead when she gets upset (i.e. Usagi giving
her a spanking (episode 60) or her fear of thunder and lightning (episode
64)), followed by a streak of yellow light into the sky. Does anyone know why
this happens?




these are the [Planetary
Symbols](https://sailormooncrystal.fandom.com/wiki/Planetary_Symbols) which as
the crystal wiki indicates

> would appear on their forehead when they awakened to their true destiny as
> Sailor Senshi, or when they performed feats of great power.

in the original anime when the Sailor Senshi were attacked their symbols would
appear which helped Luna identify that they were the reincarnation of that
Guardian, this would be the "awakened to their true destiny", eg. when Garoben
tried to force Ami to watch the brainwashing

![Ami's Planetary
Symbol](https://64.media.tumblr.com/3ee808cb5bfc2306a52b70c6d7ba7978/8fb8875ce60c2753-ad/s540x810/60a867cdfeebc0c6bbe2b58b74f1611d88134144.gif)

in the original anime you'd see Usagi's when she transforms just before her
tiara manifests. while the rest of the Senshi don't show that in the original,
in Crystal [they do the same as
Usagi](https://www.youtube.com/watch?v=3v0do3g3ZIE)

Chibi-Usa's case would all under "feats of great power" given how when she
unleashes her power during the Black Moon Arc it is generally picked up as
being a huge power spike that draws everyone's attention and/or protects
Chibi-Usa when she's in danger. one could see the Senshi's Transformation as
being a sort of regulatory system as when Usagi is able to transform properly
she stops having these outbursts of power.

for the instances when Usagi had her Symbol on her forehead while in her
Princess Serenity form, as the wiki also notes

> Sailor Moon's planetary symbol, the golden crescent moon, was worn by all
> members of the Moon Kingdom

which would be the same for Chibi-Usa however different adaptations vary if
she has one as in the Manga she can be seen with it while in the original
anime she is shown without it. the Black Moon Clan could be seen as a sort of
dark counterpart of the Senshi (or at the very least, Neo-Queen Serenity) and
thus explain their up-side down Black Crescent Moon.

