An omen would presumably cause a stir, and a hasty gathering of the community.
a public meeting
dissenting a shock
This is arguably less suitable for use in a wargame than many Triffles, but it could be incorporated directly into the tabletop action, especially in a skirmish game, with discussions taking place as factions move in or battle around. In that sense the shock announcement could be an announcement of this fact. Interacting with terrified innocents would then be an issue, and that's a difficult subject even beyond the details of simulation. It's another I hope to cover in the 'Getting out of the boat' series, at least.
In roleplaying this is a good initial event setting up the adventure, but it could be the characters themselves later on who are responsible for the rumours or who have the shock announcement to make.
In roleplaying and writing there's potential here for complex interactions between and within the crowd and leading figures, and on the fringes, perhaps barely perceptible. The key is what characters and readers know, and the way the story is moved on through the hints given. With the numbers, diversity and mixing likely at such a meeting, it's an opportunity to open new avenues in a more natural way, even without an announcement.