I think this is an excellent way to get your players into doing things together. We all know it is difficult to get many players on a shard together much less in the same place. Using event reminders like these can really help get people together. You could take it further by allowing people to use a [event command to appear close to the event if they use it within a window of time after the event is called.
Sorry thats getting a bit off-topic, I'll look into a way to announce the sigil being stolen first.
