How incredibly fortunate, then, that you just happen to have a herald in the group.
Luckily, France is more or less where "modern" heraldry started, in (I think) the eleventh and twelve centuries. Not so luckily, 1221 is still the early days of heraldry, and early heraldry tended to be simple geometric stuff).
For example: my own SCA coat of arms, which I went for early since my persona is mid-to-late 12th century French, is "Per chevron argent and Or, a chevron sable," a black chevron with white above and yellow below. The arms I came up with for the covenant in a tabletop ars campaign I was in years and years ago was "Vert, a pale wavy argent," or a green field with a white wavy stripe down the middle.
For Mons Electi's coat of arms, here's what I came up off of the top of my head in my Chamber of Concentration (best I can do at the moment, with all my resources still packed away in one of my...seventeen boxes of books stacked up in my bedroom (I think I have it narrowed down to one of eight?).
"Vert, semy of mullets and in base a mount or."
A green field, the bottom part is a yellow mountain and there are five-pointed stars strewn over the field. I was thinking that the number of stars would correspond to the current number of magi (currently seven, but could be ten after the Spring 1222 meeting).
How does that sound?
If that meets with enough approval, or we come up with something better, I'll print out a "submission form", sketch out the design, unpack my crayola markers (which I know where they are, if they've not dried out) and post something somewhere. Maybe on Obsidian Portal.