The Wikipedia article on astronomical symbols says:
The zodiac symbols are also sometimes used to represent points on the ecliptic, particularly the solstices and equinoxes.
Each symbol is taken to represent the "first point" of each sign.
Thus, ♈ the symbol for Aries, represents the March equinox; ♋, for Cancer, the June solstice; ♎, for Libra, the September equinox; and ♑, for Capricorn, the December solstice.
The article cites Roy and Clarke, Astronomy: Principles and Practice.
This question copies an example usage of ♈ and ♎ from that book.
Stellarium uses the same symbols if you set View: Markings to show the equinoxes and solstices.
$\gamma$ is a poor substitute but clear enough if ♈ is unavailable.
Since $\Omega$ stands for an orbit's longitude of ascending node (angle ♈-☉-☊), it would be a confusing substitute for ♎.
"First point of Libra" is archaic but correct.
These names and symbols represent tropical zodiac signs, not IAU constellations.
♎ is fixed at ecliptic longitude 180° regardless of constellation boundaries.
Its location in Virgo this century doesn't change its name or symbol.