I'm always on shaky ground when I talk about Greek because I can only read a tiny bit of it (mostly names) and I haven't studied the scribal abbreviations as much as Latin (the concepts are very similar, sometimes the same, but some of the shapes go in different directions and Greek has a lot of ligatures) but... even though I've suggested the shape in the rays looks like omega, more often in medieval manuscripts one would see it written as ω rather than the Ω shape.
A couple of the reasons that ω is much more common are 1) many scribes didn't bother with capital letters and 2) some scribes would enlarge the lowercase letter rather than using a different shape for the capital letters.
Now, if we consider for a moment that it might be Ω, then the choice of the shape MIGHT depend on where the person saw or learned it. For example, if they learned from manuscripts, more often they would see ω. But, if they learned from looking at old monuments (e.g., Greek sarcophagi or mosaics), then they would sometimes see ω and sometimes Ω:
So, if it is Ω then there may have been a deliberate choice to use the less common Ω shape or... maybe it's not omega.
A couple of the reasons that ω is much more common are 1) many scribes didn't bother with capital letters and 2) some scribes would enlarge the lowercase letter rather than using a different shape for the capital letters.
Now, if we consider for a moment that it might be Ω, then the choice of the shape MIGHT depend on where the person saw or learned it. For example, if they learned from manuscripts, more often they would see ω. But, if they learned from looking at old monuments (e.g., Greek sarcophagi or mosaics), then they would sometimes see ω and sometimes Ω:
So, if it is Ω then there may have been a deliberate choice to use the less common Ω shape or... maybe it's not omega.