One of my lecturers last year (a pharmacologist by training) used the symbol $\Omega ^m$ as a shorthand for equilibrium. He implied it was common practice but I've never come across it elsewhere. I was wondering if anyone else has encountered it?
I would guess $Ω^m$ notation is a personal invention and I couldn't find any sources that would standardize it.
Equilibrium contains a root from the Latin libra, meaning "weight" or "balance". As a constellation, zodiac symbol, and astrological sign, Libra is usually pictured as a set of balance scales, often held by the blindfolded goddess of justice, which symbolizes fairness, equality, and justice. Equilibrium has special meanings in biology, chemistry, physics, and economics, but in all of them it refers to the balance of competing influences.
Uppercase letter "m" is probably because $Ω^m$ is a shortened form (contruction) of a single word that ends in the same letter: equilibrium.